**This is Day 17 of 31 Days of Math Learning Success. Follow all the days here and check out others that are writing for 31 days here.**

*There are two kinds of people in the world — those who divide everything in the world into two kinds of things and those who don’t.
~Kenneth Boulding*

When I go to calculate my gas mileage, I do it twice. One way is always wrong, and one way is always right.

I know that I have to do something with the number of miles and the number of gallons. In particular, I know I have to divide them. But I can never remember which number divides by which. Or which is the *dividend* and which is the *divisor*.

But it doesn’t really matter. There’s only two numbers. And there’s only two ways to do it.

I drive 245 miles on a tank of gas that’s about 20 gallons. I know it’s either 20÷245 or 245÷20. The first one gives 0.0816, And the second one gives 12.25.

Neither of these is that desirable, I’ll admit. I drive a 1995 Chevy pickup. And I love it.

But there’s no way my gas guzzler gets 0.0816 miles per gallon. If it did, driving to the neighbor’s house would use a whole tank of gas.

So I know that the second answer, 12-ish, is the correct answer.

### Experiment with numbers.

The “translate statements to expressions” is another common “two-way” problem.

“7 less than x” screams subtraction. And as soon as you have a little experience with this, you know that it could be or . But which one?

Well, suppose is 539 (pick your favorite crazy number here). Then 7 less than 539 is 532.

So that was or .

### Try it both ways.

It’s like trying on a wedding dress. You don’t have to ** know** what dress you want. You can try them on and see which works better.

And unlike wedding dresses – there are only a few (or two) ways to do many problems.

Picking a wedding dress, well, you have bazillions.

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