5/6 or 6/7
To find what is greater lets make the fractions into decimal.
To convert fraction to decimal you have to divide the numerator ny the denominator.
5/6
⇒ 5 ÷ 6
= 0.83333333333......
6/7
⇒ 6 ÷ 7
= 0.857142.....
0.857142.... is bigger then 0.83333333333......
Therefore 6/7 is bigger then 5/7
