Tips and Techniques: Finding 100% of a Number

Given a percentage of a number, how do you find 100%? We'll show you different ways to find 100%.

First, remember that 100% means "all of it... the whole thing."

Example 1: 25% of what number is 5?

This question asks, "If 25% of a number is 5, then what is 100% of the number (the whole thing)?"

The strategy here is to see how many times the "percent number" (in this case, 25) goes into 100, and then count by that number until we reach 100-the whole thing. Here, we're told that 25% of a number is 5. So, to find 100% of the number, we count by 25s up to 100: 25, 50, 75, 100.

25% is 5, so 50% is 10, 75% is 15, and 100% is 20.

Example 2: A man spent $10.00, which was 20% of his money. How much money did he have to start?

If 20% of his money is $10.00, then 40% is $20.00. (20% + 20% = 40%)

Similarly, 60% is $30.00 (40% + 20% = 60%), 80% is $40.00, so 100% is $50.00-the amount of money the man had to start.

Here's an even faster way to approach this problem. There are 5 20%s in 100%, so this problem calls for five sets of $10.00, which equals $50.00.

Example 3: 10 kids-5% of the kids enrolled at a particular school-are out sick. How many kids are enrolled at the school?

Here, 5% is 10 kids. Since there are 20 5s in 100, we multiply 20 by 10 and get 200, the total number of students at the school.

Try these:

10% of what number is 8?

20% of what number is 4?

20% of what number is 6?

50% of what number is 28?

5% of what number is 11?

1% of what number is 2?