Que es mayor tres cuartos o tres octavos

Lets do compare both fractions, and suppose the first is greater:

3/4 > 3/8

to ease the comparison, we change the first fraction to eights:

3/4 = 6/8, lets use this:

3/4 > 3/8

6/8 > 3/8

So we can see that the left fraction, 6/8 = 3/4 is greater