How do you know where to put the "x" in the proportions?

Percent problems translate very directly from English to math. I’ll show you with an example:

The problem is, “What percent of 40 is 10?”

“What” is what you’re solving for. This should be your x.

“Per cent” – per means division, cent means 100.

“Of” – here’s a protip, in these kinds of problems, “of” means multiply.

“Is” means equals. Here’s where you put your = sign.

Now we have a translation for each and every word. The problem becomes:

x/100 * 40 = 10

And now you simply have to solve for x. Divide by 40 and multiply by 100 to get 25.

Works every time. Here’s another example:

“What is 20% of 200?”

What: x
Is: =
%: /100
Of: *

x = 20/100 * 200
x = 40

@kimchi Also use logic. Look at your answer, ask if it makes sense. That works too.