One way you can tell they are the same is if you simply 6/8, you divide both numbers by two and you get 3/4. Another way you can tell is see how many time four goes into eight. It goes in twice, so you multiply your denominator by two. My teacher taught me whatever you do to the bottom, you do to the top. So you do three times two and you get six. That's how 3/4 and 6/8 are the same.