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Percents - Problem 3


How to solve "x% of what is...? A strategy to solve percent problems is to use the proportion: is/of = %/100 ("is" over "of" equals "percent" over "100"). Fill in the known values from the given problem, and use a variable, such as x, for the unknown value. The unknown value in this kind of problem is the "of" value. Cross multiply to solve. To do this, multiply the numerator of the first fraction by the denominator of the second fraction and set it equal to the denominator of the first fraction times the numerator of the second fraction (is * 100 = of * %). Then solve for the unknown value (the variable).

So let's take a look at another percents problem. 5% of what number is 60.

We can solve this using our short cut proportion which if you remember says over of is equal to the percent over 100. So if you read the question it says, 5% so we know that 5 is going to go over 100 of what number? Well of what is the variable that we're looking for? So of is going to be x and the number that we're given is 60.

Now we simply cross multiply. 100 times 60 is 6000 and x times 5, that's just 5x. Now we divide by 5 on both sides and you're left with x equals 1200 and if you're having trouble with these kinds of problems just remember this shortcut proportion and it will get you started right every time.

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