Why is 7/8 greater than 6/7

Well to compare with the same denominator, it will be easier to see which is bigger or smaller.

7/8 = 49/56

6/7 = 48/56.

Now we can see why 49/56 or 7/8 is greater than 48/56 or 6/7 simply by looking at the top numbers or the numerators of the 2 fractions.