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rico12 · Nov 14, 2011, 05:05 PM

Assuming a steady speed of 50 miles per hour,how long will it take to go 350 miles?

Wondergirl · Nov 14, 2011, 05:08 PM

Divide.

rico12 · Nov 14, 2011, 05:12 PM

I have to set up a proportion , and I don't know how.

J_9 · Nov 14, 2011, 05:15 PM

How did they show you in school?

Wondergirl · Nov 14, 2011, 05:19 PM

Set up two divisions with an equals sign in between.

Ergo:

3/4 = 6/8 is an example of a proportion.

When one of the four numbers in a proportion is unknown, cross products may be used to find the unknown number. This is called solving the proportion. Question marks or letters are frequently used in place of the unknown number.

x/4 = 6/8

Do the same with your problem.

jcaron2 · Nov 15, 2011, 03:15 PM

By the way, just to add a little to what others said above, there are several keywords that you'll see in word problems throughout your school career that translate directly from english into "math". The word "per" is one of them. It means "divided by". For example, if your dog barks 42 times per day, that means (42 barks) $\div$ (1 day). If you then wanted to know how many times your dog barks in 30 days, you'd recognize that the ratio of barks per day (i.e. # of barks divided by # of days) remains equal. Thus:

$\frac{42 \; barks}{1 \; day}=\frac{x \; barks}{30 \; days}$

Then you just have to solve for x.

The problem you have here is very similar, except instead of barks per day, you're dealing with miles per hour. Also, the unknown you're solving for will end up in the denominator in this case (it's hours your looking for, not miles). Otherwise, it's just like Wondergirl said.