In a fraction, the number above the line is called the numerator, and the number below the line is called the denominator. The fraction shows how many “pieces” of the number there are, compared to how many there are possible. For instance, in the fraction 78/80, we could say that there are 78 pieces out of a possible 80 pieces.
“Percent” means “per hundred”, so for percentages we want to know how many pieces there are if there are 100 pieces possible. For example, if we look at the percentage 75%, that means we have 75 pieces of the possible 100. Re-writing this in fraction form, we see 75/100.
When converting the fraction into a percent, the first step is to adjust the fraction so that there will be 100 pieces possible (the denominator needs to be changed to 100). To do this, you first divide 100 by the denominator:
We can then adjust the whole fraction using this number, like so:
As you can see, there are 97.5 pieces out of a possible 100 pieces. Re-writing this as a percentage, we can see that 78/80 as a percentage is 97.5%.