# Is my solution to this puzzle reasonable? **URL:** \ **Category:** Factual Questions\ **Created:** [June 10, 2019, 10:48am UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289 "2019-06-10T10:48:12Z")\ **Posts on this page:** 20\ **Page:** 5
**Author:** ![BillGates](https://avatars.discourse-cdn.com/v4/letter/b/d26b3c/32.png) [@BillGates](https://boards.straightdope.com/u/BillGates)\ **Post date:** [June 12, 2019, 6:08pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/81 "2019-06-12T18:08:42Z")
Strangely, there’s no mention of the kidnappers leaving behind a way to contact them, so even if a ransom was arranged, how would they know (when) to come back and rescue you? Theoretically they could somehow reach out to every person you know that you might make your call(s) to, but that doesn’t seem reasonable or likely. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 12, 2019, 6:16pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/82 "2019-06-12T18:16:06Z")
> [@BillGates](#): > > Strangely, there’s no mention of the kidnappers leaving behind a way to contact them, so even if a ransom was arranged, how would they know (when) to come back and rescue you? Theoretically they could somehow reach out to every person you know that you might make your call(s) to, but that doesn’t seem reasonable or likely. I assume if the ransom is paid they’ll reveal your location, maybe. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 12, 2019, 6:18pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/83 "2019-06-12T18:18:46Z")
Presumably the kidnappers know who your next of kin is, and have contacted them separately. And if you call any of “your people” to tell them you want them to ransom you, they’ll spread the word. You’re not the one paying the ransom, so you don’t need to know how to contact the kidnappers. ---
**Author:** ![Sigene](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@Sigene](https://boards.straightdope.com/u/Sigene)\ **Post date:** [June 12, 2019, 8:37pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/84 "2019-06-12T20:37:20Z")
> [@MrDibble](#): > > Eh? Do you think ocean islands can’t have sand? Plenty that do. [Here’s one](https://en.wikipedia.org/wiki/Assumption_Island). My apologies, I wasn’t clear. The riddler indicates that the island is “all flat sand”, no rock, no coral, no caves etc. like assumption island. So, Yes, I’m confident ocean islands can have sandy beaches, but that isn’t what is described in the text. My point is that an “all flat sand” island would not likely be in deep ocean but rather in fairly shallow water. Therefore, if it is in shallow water, I assumed, if in the ocean, it would have significant tides. Again my knowledge of tides in shallow areas of the ocean where sand islands could exist is not strong, but I assume they would have noticeable tides. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [June 12, 2019, 8:52pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/85 "2019-06-12T20:52:57Z")
If you need to call in the morning (as the puzzle sort-of implies), then what’s wrong with finding rough North by the movement of the stars, along with a rough latitude from the elevation of the center of movement; and calling at Sunrise to get a pretty good longitude, along with another rough latitude from the direction of sunrise? In general, I’d consider calling at sundown instead, mostly so I could look around and see if there are any other islands visible, but also to get a more accurate latitude (mostly by getting a good east-west line from shadows, which will allow a more accurate bearing on sunset). But even with the morning call, my rough estimate is that the longitude will be within 10 miles or so, and the latitude probably a couple hundred. Which, given that the search is for a clearly visible island, should be good enough, right? ---
**Author:** ![excavating\_for\_a\_mind](https://avatars.discourse-cdn.com/v4/letter/e/e8c25b/32.png) [@excavating\_for\_a\_mind](https://boards.straightdope.com/u/excavating_for_a_mind)\ **Post date:** [June 12, 2019, 10:53pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/86 "2019-06-12T22:53:30Z")
A few things I find curious about the initial conditions. Your “host” supplies you with four sandwiches and 4 pints of water, which is “enough for a few days.” Now, most references I find on-line say a person will die in a few days without water, and that a person should expect to need at least two quarts per day, more in hot conditions. Now, you are on a desert island with no shade. The night sky is clear, which would suggest that you will have a cloudless day. I would expect a person exposed to the sun all day to need every bit of those 4 pints the first day. He might be able to survive on two pints per day, but he wouldn’t be in very good condition after two days. To me, “a few days” suggests at least three, perhaps four, days. Lack of any vegetation on the island strongly suggests that there is no fresh water available. As has been mentioned, the restriction on not calling “before daylight” is strange. My guess is this restriction is a hint, but perhaps it is merely obfuscation. The sandwiches are interesting. Liverwurst and peanut butter on Rye. Another hint, or just obfuscation? Sure, liverwurst and peanut butter will have high protein and calorie, but if it’s just a few days, it really wouldn’t make that much difference if it was watercress and tomato. As mentioned, water is the big problem. A few days without food will make you very hungry, but it won’t kill you (like a day without water in the sun can). Waving at the surf and saying “that’s salt” is also odd. One would expect salt water if the island was on an ocean, and it is easy to determine (which the marooned man does, in fact, do), so why does the kidnapper mention it? I would imagine that “Your knowledge of astronomy is too weak to try to estimate your location by the stars” means that even locating Polaris is not in your skill set. That is, the intended solution does not involve looking at the stars. The exactly one minute restriction on the battery is a bit strange. I understand it is a common device to limit phone use, but in real life, I don’t think you could get that kind of accuracy in the amount of time on the phone. Finally, without knowing east from west, north from south, before daybreak you have figured out what to do. The only suggestion made in this thread that seems to work for me is to call right at sunrise and tell them that you are on a desert island, the size of the island, that the sun is rising right now, and you will call again when the sun sets. Yes, this wouldn’t work well close to an equinox, but the starting conditions seem to rule that out to begin with… ---
**Author:** ![Sigene](https://avatars.discourse-cdn.com/v4/letter/s/df788c/32.png) [@Sigene](https://boards.straightdope.com/u/Sigene)\ **Post date:** [June 13, 2019, 2:08am UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/87 "2019-06-13T02:08:58Z")
I also note that there is no “requirement” that the call is made on the first daybreak. This is just an assumption that ‘at daybreak’ means the first one. I wonder if there is advantage to wait an entire day, to get more information like the altitude of the sun at noon, and make the call on the next daybreak. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [June 13, 2019, 2:29am UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/88 "2019-06-13T02:29:33Z")
> [@Sigene](#): > > My point is that an “all flat sand” island would not likely be in deep ocean but rather in fairly shallow water. You’re right. An island as described in the puzzle will be somewhere near a large land mass. Out in the open ocean, wind and waves (especially storms) will wash such an island away. Near continents and large islands, waves wash the sand down the coast in one direction. That means they will bring about as much sand to the island as they take away, so such islands are stable. (This is ignoring man-made structures such as jetties, which interfere with the natural movement of sand.) ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [June 13, 2019, 8:44am UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/89 "2019-06-13T08:44:07Z")
I read that as “all flat sand” as a covering as opposed to plants, but I see what you’re saying. ---
**Author:** ![N9IWP](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/n9iwp/32/3154_2.png) [@N9IWP](https://boards.straightdope.com/u/N9IWP)\ **Post date:** [June 14, 2019, 12:35pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/90 "2019-06-14T12:35:19Z")
So my solution was correct: > **[How Inefficient Can You Make Your Walk To Class?](https://fivethirtyeight.com/features/how-inefficient-can-you-make-your-walk-to-class/)** > > Welcome to The Riddler. Every week, I offer up problems related to the things we hold dear around here: math, logic and probability. There are two types: Riddle… Specifically mentioned that is WASN"T equinox season Brian ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [June 14, 2019, 5:44pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/91 "2019-06-14T17:44:36Z")
I will argue that you can’t determine hemisphere by whether the shadow is to the north or south of the bottle; instead you can determine whether you are north or south of whichever latitude line has the noon sun directly overhead for that date. There may be a more elegant way of putting that. This line of latitude varies from the Tropic of Capricorn to the Tropic of Cancer depending on the date. So, on June 21st (summer solstice) if the shadow at noon is pointing south, the most that you can say is that your latitude is somewhere between ~23.5 deg North, and 66.5 deg South (any further South on that date and the Sun wouldn’t ever rise). But on December 22nd, if the noon shadow was pointing South, you would say that you were between ~23.5 deg South and 66.5 deg S (again, any farther South and the Sun wouldn’t have ever set). Those of us who live in the mid- or- high-latitudes get used to the Sun always moving across the same half of the sky, year-round. But in the Tropics, sometimes it’s in the North and sometimes it’s in the South. Further quibble: there’s nothing in the original question to prove that it isn’t near the equinoxes; there are plenty of places in the world where it could be snowy around the vernal or autumnal equinoxes. [Youtube example.](https://www.youtube.com/watch?v=NZZczdMurg0) ---
**Author:** ![TokyoBayer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tokyobayer/32/13989_2.png) [@TokyoBayer](https://boards.straightdope.com/u/TokyoBayer)\ **Post date:** [June 15, 2019, 5:16am UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/92 "2019-06-15T05:16:44Z")
> [@brossa](#): > > I will argue that you can’t determine hemisphere by whether the shadow is to the north or south of the bottle; instead you can determine whether you are north or south of whichever latitude line has the noon sun directly overhead for that date. There may be a more elegant way of putting that. This line of latitude varies from the Tropic of Capricorn to the Tropic of Cancer depending on the date. So, on June 21st (summer solstice) if the shadow at noon is pointing south, the most that you can say is that your latitude is somewhere between ~23.5 deg North, and 66.5 deg South (any further South on that date and the Sun wouldn’t ever rise). But on December 22nd, if the noon shadow was pointing South, you would say that you were between ~23.5 deg South and 66.5 deg S (again, any farther South and the Sun wouldn’t have ever set). Actually, they are correct. They are only discussing using the direction of the shadow on the special case of an equinox. > [@](#): > > Had you been kidnapped at equinox season, when daylight has the same duration the world over, finding your latitude would be more involved, requiring, for example, finding the ratio between a shadow’s length and the height of a water bottle at noon, and identifying the hemisphere by which side of the bottle the shadow extends from (north or south). This also addresses your second point about determining latitude, which can be done can be found by the length of the bottle’s shadow at noon. No shadow means [del] that there are six more weeks of winter [/del] that you are on the equator. The increasing length of the shadow as a ratio of the height of the bottle will tell you your latitude. ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [June 15, 2019, 7:40pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/93 "2019-06-15T19:40:15Z")
Rereading that, I will grant that it can be read as applying only to equinox dates, which would be correct. I was reading the clause ‘finding your latitude would be more involved…’ as being true in general, which is not correct. And their statement about a snowy night doesn’t demonstrate that it isn’t near an equinox, so the ‘call at dawn and dusk only’ can’t be guaranteed to give your latitude anyway. ---
**Author:** ![kaylasdad99](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kaylasdad99/32/3398_2.png) [@kaylasdad99](https://boards.straightdope.com/u/kaylasdad99)\ **Post date:** [June 16, 2019, 8:22am UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/94 "2019-06-16T08:22:20Z")
Why would the kidnappers tell their victim to wait until sunrise to place the call? They’re terrorists/extortionists; they have no plausible motivation to give their victim a “sporting chance”… Unless the satellite phone only works during daylight hours (which strikes me as kinda ridiculous, even though I have virtually ZERO knowledge of satellite phones and their workings). ---
**Author:** ![TokyoBayer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tokyobayer/32/13989_2.png) [@TokyoBayer](https://boards.straightdope.com/u/TokyoBayer)\ **Post date:** [June 16, 2019, 9:28am UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/95 "2019-06-16T09:28:38Z")
> [@brossa](#): > > And their statement about a snowy night doesn’t demonstrate that it isn’t near an equinox, so the ‘call at dawn and dusk only’ can’t be guaranteed to give your latitude anyway. I didn’t read that the comment about the snowy night as proving it wasn’t near an equinox. ISTM that it was just more extraneous information. The person being kidnapped would know if it’s near the equinox. They provided a method of solving for both the case of not near an equinox and hinted at the more complicated solution for the other. ---
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [June 16, 2019, 3:13pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/96 "2019-06-16T15:13:04Z")
Not sure if I figured right but I calculated each second on the clock as covering about 3.5 longitudinal miles? So depending on how accurately the observer got his sunrise time correct, how accurately the listener noted it, and the phone delay, the margin of error could be rather large. Being 5 seconds off the exact time gives you 17 miles to search. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [June 16, 2019, 4:08pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/97 "2019-06-16T16:08:01Z")
> [@Hampshire](#): > > Not sure if I figured right but I calculated each second on the clock as covering about 3.5 longitudinal miles? . That sounds wrong. Consider the Earth’s circumference is about 25000 mi and there are 86400 sec/day. A second should be around .3 miles. You may have slipped a decimal point in your calculations. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [June 16, 2019, 4:29pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/98 "2019-06-16T16:29:11Z")
> [@kaylasdad99](#): > > Why would the kidnappers tell their victim to wait until sunrise to place the call? They’re terrorists/extortionists; they have no plausible motivation to give their victim a “sporting chance”… Because this is a brain teaser and not a real-life situation? I mean, why do Bond villains have such complicated methods of attempting to kill 007 that allow him a way out? It’s all fiction. Don’t fight the hypothetical. ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [June 16, 2019, 8:18pm UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/99 "2019-06-16T20:18:25Z")
The title of the riddle asks “can you escape at dawn?” Calling once at sunrise and then later at sunset makes the answer to this as no, at least not by dawn on the first morning. ---
**Author:** ![Kedikat](https://avatars.discourse-cdn.com/v4/letter/k/ed655f/32.png) [@Kedikat](https://boards.straightdope.com/u/Kedikat)\ **Post date:** [June 17, 2019, 12:44am UTC](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289/100 "2019-06-17T00:44:36Z")
You could tear a long strip of paper bag, if you do it somewhat spiral. Plant a water bottle before sunrise. Mark off the end of the shadow when it equals the length of your paper tape. Mark the opposite point at sunset. Using the paper tape and the water bottle as the center. Do some very basic geometry in the sand of intersecting arcs. This will give you a 90 degree line from the east West line. Noon at your location. If you are not at the Equator. The North South offset of your arc intersections may also help in Latitude estimate. The North intersection being X percent longer than the South one or opposite. Wait till local noon and tell them that when you make the call. You suck at navigation. But for some reason you paid attention in geometry. As the sat phone makers also seemed to pick and choose abilities of their system. [Previous page](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289.md?page=4) [Next page](https://boards.straightdope.com/t/is-my-solution-to-this-puzzle-reasonable/835289.md?page=6)