if you multiply a number by 1, you get the same number, right? 2/2 is equal to 1, right? so, 4/7 * 2/2 = 4/7, because you're just multiplying 4/7 by 1.

by multiplying by a fraction that was equivalent to 1, you made an equivalent fraction. in other words, you multiplied the top and the bottom by the same number.
so:
4/7
= 8/14
= 12/21
= 16/28
et cetera