Question

How can you compare 2 fractions by using a number

Answer 1

I don't know what you're asking here but maybe this is referring to ratios. For example:

1/2 and 3/2 have a ratio of 1:3

Answer 2

Or you could say 3/2 is 3 times greater than 1/2. You're comparing the two fractions with the number '3'. Maybe if you clarify your question I could be more helpful.