Expressing a Quantity as a Percentage

Let’s say a class has 40 students and 13 bring packed lunch. What percentage is that? Well first we write it as a fraction — 13 over 40.

Now the fraction line just means divide. So 13 over 40 means 13 divided by 40. Type it into your calculator. 13, divide, 40, equals. You get zero point three two five. That’s the decimal.

Now to get the percentage, shift the decimal point two places to the right. Thirty-two point five percent.

Now let’s try a messier one. A factory produces 16 batches. 7 passed quality control. What percentage passed? 7 out of 16 gives us 7 over 16.

The fraction line means divide, so type 7, divide, 16, equals. Zero point four three seven five. That’s a four-digit decimal!

Now shift the decimal point two places. Forty-three point seven five percent.

Now let’s look at a percentage increase. Someone’s pay goes from twenty-five dollars an hour to thirty-two dollars an hour. What percentage did their pay increase by? First, find the increase. Thirty-two minus twenty-five is seven dollars. Now we write the increase as a fraction of the original — 7 over 25.

Now divide. 7 divided by 25. Type it in. 7, divide, 25, equals. Zero point two eight. That’s the decimal.

Shift the decimal point two places to the right. Twenty-eight percent. Their pay increased by twenty-eight percent.