Ginger's baby weighed only 3 3/8 pounds when it was born. the doctor said it could not leave the hospital until it weighed 5 1/2 pounds. how many pounds must the baby gain before it can go home to ginger ?

To subtract 3 3/8 from 5 1/2,
by turning into fractions
[(5x2)+1]/2 = 11/2
[(3x8)+3]/8 = 27/8
 11/2 - 27/8
To subtract fractions, your denominator needs to have the same number. so multiply it by 4
 44/8 - 27/8 = (44-27)/8 = 17/8.
17 / 8 pounds or 2 and 1/8 because 17 / 8 = 2 remainder 1. 
In terms of weight that is 2.125 pounds.