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Working with Percentages Examples

Example 1

What's 80% of 40?
Our first proportion is the percentage. 80% means 80 out of 100.
We need to find 80% of 40, so 40 is a denominator. Now we solve for x. Multiply both sides by (100)(40) to obliterate those denominators.
Divide by the coefficient of x.
So 80% of 40 is 32. Noice.

Example 2

30% of what number is 15?
First things first, y'all. Our first proportion is the percentage. 30% means 30 out of 100.
We need to find 30% of some number x, so x is a denominator this time. Then we multiply both sides by 100x. So long, denominators.
Awesomesauce. Finish up by dividing both sides by 30.
Nailed it. 30% of 50 is 15.

Example 3

What percent of 60 is 20?
Our first proportion is the percentage. We don't know our % this time, so it's our unknown, x.
20 is some unknown part of 60, so that's a ratio of 20:60. Everything's all set up, so we're ready to solve for x. Multiply both sides by (100)(60).
Solid. Now divide by 60 to get x by itself.
There we go: our missing percent is 33.333...%.

Example 4

What's 90% of 5?
Let's use the equation method this time. First we convert 90% into a decimal by bopping the decimal point to the left two places. 90% = 0.9
Now translate the equation. What (x) is (=) 90% of (multiply) 5? x = 0.9 × 5
No shame in using a calculator. x = 0.9 × 5 = 4.5

Example 5

What's 9% of 300?
We're gonna go with the equation method again. First convert 9% to a decimal. The decimal point boogies two spots to the left. 9% = 0.09
Translation time. What's 9% of 300? x = 0.09 × 300
All that's left is the actual multiplying. x = 0.09 × 300 = 27