You start off by finding common denominators. To do that we first have to take 1 1/2 and change it to 3/2 and you get that by adding 1/2 to 2/2, which is equal to 1. Then you have to get your denominator of 2 to be equal to your denominator of 4 , so we do that by multiplying the top and bottom of 3/2 by 2 . giving us 6/4 . then it is a simple subtraction problem , 6/4 - 3/4 , and from that we subtract across getting 3/4 .