When two fractions refer to the same whole and have the same denominator explain why you can compare only the numerator

It depends on the way they look like because if you have the denominators as the same number and if it is you can just use that same nu!ber

If the diameter is 8 than the radius is 4 because 2r or 2*radius equals the diameter. 4*2=8. 8/2=4.