# Give me some math problems

**URL:** <https://boards.straightdope.com/t/give-me-some-math-problems/513062>\
**Category:** Miscellaneous and Personal Stuff I Must Share\
**Created:** [October 8, 2009, 4:41pm UTC](https://boards.straightdope.com/t/give-me-some-math-problems/513062 "2009-10-08T16:41:49Z")\
**Posts on this page:** 3\
**Page:** 5

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**Author:** ![Chessic\_Sense](https://avatars.discourse-cdn.com/v4/letter/c/7c8e57/32.png) [@Chessic\_Sense](https://boards.straightdope.com/u/Chessic_Sense)\
**Post date:** [October 15, 2009, 7:57pm UTC](https://boards.straightdope.com/t/give-me-some-math-problems/513062/81 "2009-10-15T19:57:42Z")

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Are you clear on unit conversion? Using my helpful word hints, you can see that “miles per hour” really means Miles / hours. So if I tell you you went 37 miles in 1.5 hours, then the calculation is easy: 37/1.5 = 24.7 mph.

But what if I said it was 50 minutes instead? Then you can still divide, but you’ll get – what, class? – yes, miles per minute. So you can either get miles/minute and convert it to MPH or you can convert 50 minutes to hours, then do the division. The choice is yours.

All you have to do is line up the units so that they cancel out and you’re left with what you want:

Miles/minute \* minutes/ hour = miles/hour. Why did I choose min/hr and not hr/min, or something else? Because I want one “minute” on the top and one “minute” on the bottom so that they cancel.

Is that clear and easy enough? Do you understand that? It’s important for a lot of word problems.

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**Author:** ![ivylass](https://avatars.discourse-cdn.com/v4/letter/i/9de053/32.png) [@ivylass](https://boards.straightdope.com/u/ivylass)\
**Post date:** [October 15, 2009, 8:01pm UTC](https://boards.straightdope.com/t/give-me-some-math-problems/513062/82 "2009-10-15T20:01:29Z")

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It is when you explain it like that…thanks!! I’ve saved your cheats and will keep them with my review.

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**Author:** ![Mtgman](https://avatars.discourse-cdn.com/v4/letter/m/b5a626/32.png) [@Mtgman](https://boards.straightdope.com/u/Mtgman)\
**Post date:** [October 15, 2009, 8:53pm UTC](https://boards.straightdope.com/t/give-me-some-math-problems/513062/83 "2009-10-15T20:53:38Z")

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> [@Chessic\_Sense](#):
>
> You used the diameter as the radius.

I’m not seeing it. I wrote out my answer using words in most places, but I came up with 4.5 for the radius of the normal layers. I also came up with the same final diameter for the large cake pan as you(and **L. G. Butts, Ph.D.** , and **Baker** the second time around) did, disregarding rounding differences. Where did I use the diameter instead of radius?

Enjoy,  
Steven

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