First let's make the denominators of the fractions equal.
To do this, we have to find a number which both 5 and 7 divide into.
The smallest number that does this is 35.
2 --> Multiply the numerator by 7
--
5 --> Multiply the denominator by 7 to get 35
= 14/35
1 --> Multiply the numerator by 5
--
7 --> Multiply the denominator by 5 to get 35
= 5/35
Joe has eaten 14/35 and James has eaten 5/35.
14 / 5 = 2.8
Joe has eaten 2.8 (or 2 4/5) times more pizza than James.