Question

find the four
rational number between 3/4 and 4/5

Answer 1

write five rational number between 4/5 and 3/4?

Simple

45=16a20a

34=15a20a

For any (rational) a≠0

All you need to do is to big an a large enough ( a>5 in this case) and you can put as many numbers between them as you like. An other way to see that there are infinite many rationals between them (as for any pair of distinct rationals) is this:

∀a,b∈Q(a<b⟹a<a+b2<b)