# Simple Math Question **URL:** \ **Category:** Factual Questions\ **Created:** [November 9, 2009, 7:33pm UTC](https://boards.straightdope.com/t/simple-math-question/516928 "2009-11-09T19:33:19Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Jake](https://avatars.discourse-cdn.com/v4/letter/j/f475e1/32.png) [@Jake](https://boards.straightdope.com/u/Jake)\ **Post date:** [November 9, 2009, 7:33pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/1 "2009-11-09T19:33:19Z")
“My friends and I were on a beer run and noticed that the cases were discounted 10%. Since it was a big party, we bought 2 cases. The cashier multiplied 2 times 10% and gave us a 20% discount” I can’t see anything wrong with this. If she gave a 20% discount for two cases wouldn’t it come out to 10% for each case? 😕 =“[http://home.tiac.net/~cri/2007/amongus.html](http://home.tiac.net/~cri/2007/amongus.html)” ---
**Author:** ![Syzygy](https://avatars.discourse-cdn.com/v4/letter/s/bc79bd/32.png) [@Syzygy](https://boards.straightdope.com/u/Syzygy)\ **Post date:** [November 9, 2009, 7:37pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/2 "2009-11-09T19:37:14Z")
The original discount was 10% off, or 0.9x, where x is the cost of one case. If you purchased 2 cases at 10% discount, the total is 0.9(2x), or 1.8x. What she gave you was 0.8(2x), or 1.6x. So you made out, is what I’m saying. ---
**Author:** ![Munch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/munch/32/5281_2.png) [@Munch](https://boards.straightdope.com/u/Munch)\ **Post date:** [November 9, 2009, 7:42pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/3 "2009-11-09T19:42:58Z")
> [@Jake](#): > > “My friends and I were on a beer run and noticed that the cases were discounted 10%. Since it was a big party, we bought 2 cases. The cashier multiplied 2 times 10% and gave us a 20% discount” Substitute 50% instead of 10% in your above scenario and see if it still makes sense. ---
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [November 9, 2009, 7:43pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/4 "2009-11-09T19:43:42Z")
[http://home.tiac.net/~cri/2007/amongus.html](http://home.tiac.net/~cri/2007/amongus.html) Here’s the link. Agree with \*\*syzygy \*\*- she could have multiplied the dollar discount for one case by two and been alright, but she multiplied the discount percentage by two and applied it to both cases. ---
**Author:** ![Scarlett67](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scarlett67/32/7387_2.png) [@Scarlett67](https://boards.straightdope.com/u/Scarlett67)\ **Post date:** [November 9, 2009, 7:44pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/5 "2009-11-09T19:44:00Z")
Say regular price of a case is $10. 10% off each case makes the price $9, time 2 equals $18 for both cases. 20% off 2 cases makes the price $8 + $8, or $16 for both cases. The cashier screwed up. You multiply the percentage off times the total price, not the number of cases. If you’d bought 10 cases, would she have given them to you for free (10% off times 10 cases = 100% off?) ---
**Author:** ![Whiteknight](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whiteknight/32/4962_2.png) [@Whiteknight](https://boards.straightdope.com/u/Whiteknight)\ **Post date:** [November 9, 2009, 7:44pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/6 "2009-11-09T19:44:15Z")
> [@Munch](#): > > Substitute 50% instead of 10% in your above scenario and see if it still makes sense. Or better yet, just buy 10 cases next time. ---
**Author:** ![Giles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giles/32/60_2.png) [@Giles](https://boards.straightdope.com/u/Giles)\ **Post date:** [November 9, 2009, 7:44pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/7 "2009-11-09T19:44:19Z")
I’d ask the cashier what the discount would be if I bought 10 cases – or, better still, more than 10 cases. Alternatively, if you didn’t want to be too greedy, you could just but 9 cases for the price of one. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [November 9, 2009, 7:48pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/8 "2009-11-09T19:48:25Z")
The discount percentage should not increase with the number of cases as you describe; if it did, then 10 cases would mean you’d get 100% off, i.e. a shitload of beer absolutely free of charge. If you buy each case separately (for 10% off), that’s the same as buying both cases together for 10% off of the grand total. 2 \* (0.9X) = 0.9 \* (2X) Where X = the regular price of a case of beer. As Syzygy noted, if you got 20% off for buying two cases, you got an extra good deal. ---
**Author:** ![Jake](https://avatars.discourse-cdn.com/v4/letter/j/f475e1/32.png) [@Jake](https://boards.straightdope.com/u/Jake)\ **Post date:** [November 9, 2009, 7:50pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/9 "2009-11-09T19:50:35Z")
> [@bup](#): > > [http://home.tiac.net/~cri/2007/amongus.html](http://home.tiac.net/~cri/2007/amongus.html) > > Here’s the link. Agree with \*\*syzygy \*\*- she could have multiplied the dollar discount for one case by two and been alright, but she multiplied the discount percentage by two and applied it to both cases. I think I get it Bup. She applied a 20% discount to each case! Thanks All. They say that the mind is the first thing to go… :smack: ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [November 9, 2009, 8:29pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/10 "2009-11-09T20:29:32Z")
Buy 100 cases, get a free store! ---
**Author:** ![AWB](https://avatars.discourse-cdn.com/v4/letter/a/bb73d2/32.png) [@AWB](https://boards.straightdope.com/u/AWB)\ **Post date:** [November 9, 2009, 9:43pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/11 "2009-11-09T21:43:09Z")
I had a friend back when I was 20 and he was 19. We were having lunch at a restaurant/bar. On a whim that the waitress wouldn’t card him, he ordered a beer. She did card him, but she goofed on the subtract/borrow procedure when she subtracted 1965 from 1984 and got 21. I then ordered one (before we figure out her mistake). But 1984-1964 is more easily seen to be 20, so no beer for A. ---
**Author:** ![MovieMogul](https://avatars.discourse-cdn.com/v4/letter/m/f08c70/32.png) [@MovieMogul](https://boards.straightdope.com/u/MovieMogul)\ **Post date:** [November 9, 2009, 11:50pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/12 "2009-11-09T23:50:05Z")
> [@Jake](#): > > Thanks All. They say that the mind is the first thing to go… > :smack: Take comfort: you might be wrong, and it was actually looks that were the first to go. 😃 ---
**Author:** ![sunacres](https://avatars.discourse-cdn.com/v4/letter/s/4491bb/32.png) [@sunacres](https://boards.straightdope.com/u/sunacres)\ **Post date:** [November 10, 2009, 12:00am UTC](https://boards.straightdope.com/t/simple-math-question/516928/13 "2009-11-10T00:00:05Z")
> [@Jake](#): > > I think I get it Bup. She applied a 20% discount to each case! Just like my students - still doesn’t get it! ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [November 10, 2009, 12:25am UTC](https://boards.straightdope.com/t/simple-math-question/516928/14 "2009-11-10T00:25:55Z")
> [@Jake](#): > > She applied a 20% discount to each case! Because of the way multiplication works, yes, she did. But only incidentally. ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [November 10, 2009, 3:05am UTC](https://boards.straightdope.com/t/simple-math-question/516928/15 "2009-11-10T03:05:10Z")
> [@sunacres](#): > > Just like my students - still doesn’t get it! Am I being whooshed? He got it. ---
**Author:** ![Iridescent\_Orb](https://avatars.discourse-cdn.com/v4/letter/i/9de053/32.png) [@Iridescent\_Orb](https://boards.straightdope.com/u/Iridescent_Orb)\ **Post date:** [November 10, 2009, 6:03am UTC](https://boards.straightdope.com/t/simple-math-question/516928/16 "2009-11-10T06:03:40Z")
Next time do the math before you drink the two cases. 😉 ---
**Author:** ![Mosier](https://avatars.discourse-cdn.com/v4/letter/m/7ea924/32.png) [@Mosier](https://boards.straightdope.com/u/Mosier)\ **Post date:** [November 10, 2009, 8:44am UTC](https://boards.straightdope.com/t/simple-math-question/516928/17 "2009-11-10T08:44:58Z")
> [@Jake](#): > > “My friends and I were on a beer run and noticed that the cases were discounted 10%. Since it was a big party, we bought 2 cases. The cashier multiplied 2 times 10% and gave us a 20% discount” > I can’t see anything wrong with this. If she gave a 20% discount for two cases wouldn’t it come out to 10% for each case? 😕 > =“[http://home.tiac.net/~cri/2007/amongus.html](http://home.tiac.net/~cri/2007/amongus.html)” So if you buy 10 cases, they’re free! What happens when you buy 11 cases? The mind boggles. ---
**Author:** ![muttrox](https://avatars.discourse-cdn.com/v4/letter/m/a8b319/32.png) [@muttrox](https://boards.straightdope.com/u/muttrox)\ **Post date:** [November 10, 2009, 2:42pm UTC](https://boards.straightdope.com/t/simple-math-question/516928/18 "2009-11-10T14:42:29Z")
What if you get 11 cases? Reminds me of [Tippy Turtle.](http://snltranscripts.jt.org/84/84btippiturtle.phtm) > [@](#): > > Tippi Turtle: Hi, everybody! Well, enough small talk - we’ve got people to annoy! Today, we’re gonna bother these guys - the hammerheads at the U.S. Post Office. Hee hee hee! Now, pay attention. > > [Tippi demonstrates in his home workshop] > > Get some real thin balsa wood, and glue it together like this. See? You make a little box! Then, you take a helium balloon and you put it inside like this. Then, wrap it up and address it! Take it downtown. > > [show Tippi Turtle standing in line at the Post Office] > > Hee hee hee! This is gonna be great! [jumps excitedly] > > Postal Employee: Next. > > Tippi Turtle: Yes. Good afternoon, Mr. United States Post Office Man. Now, you charge according to weight, is that correct? > > Postal Employee: Yeah, yeah, yeah, just put it on the scale. > > Tippi Turtle: Okee-dokee! [places his box on the scale, but it floats upward] Looks like you owe me some money, hammerhead!