Question

What's bigger 9/10 or 4/5

Answer 1

To be able to compare 2 fraciton we have to make common denominator and then we can just compare numerators. 
$\frac{4}{5}= \frac{4*2}{5*2}= \frac{8}{10}$
Now we can compare numerator from the first (9) and from the second fraction (8)
9>8, so the bigger is 9/10

Answer 2

9/10 because smaller pieces and has more of them