66/78 as a percentage is 84.62%. This number tells you how much of a whole the fraction represents when it’s expressed in percent form.
The fraction 66/78 can be reduced by dividing both the numerator and denominator by their greatest common divisor, 6. Doing this gives the simpler fraction 11/13, which still corresponds to the same 84.62% when converted.
Knowing the percent value makes it easy to compare this part to other percentages. For example, it’s a little lower than 90%, but higher than 80%, giving a quick sense of size without having to work with the original fraction.
