Lets see if the next procedure can explain what you need:
Try have A contain, for example, 100
B has 20% more: 20% is 20/100 or 0.20
20% of 100 = 0.02*100= 20
so B has 100+20 = 120
to make the number equal you want to move 10 from B to A so both have
110
I Hope this can help you
