Find the Rate
The word percent (per + cent) means per 100. The symbol % looks like its meaning /100. You can replace the % symbol in any problem with /100.
There are 3 general types of percent problems which you'll often encounter.
- Find the part (also called the percentage).
- Find the rate.
- Find the whole (also called the base).
Let's look at the second type: Find the rate. Here's an example problem.
At a manufacturing plant, a quality control technician randomly tests 200
products. If 5 out of 200 failed, find the failure rate.
Again it helps to look at how the 3 variables are related: P = R•W. This time let's solve for the rate, R, in terms of the part and the whole. Divide both sides of the equation by W. We get:
R = P/W where R is the Rate, P is the part, and W is the whole.
The Rate is equal to the Part divided by the Whole. In this problem, the whole is 200 and the part is 5. So P/W = 5/200 = 1/40 = .025 or 2½%. So the failure rate is 2½%.
Now try it on your own!
Find the rate.
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