The ratio of Joe's CDs to Peggy's CDs was 5:3. After Joe gave Peggy half of her CDs, Peggy had 18 more CDs than started with. How many CDs did Peggy get from Joe?

Let Joe's CDs =J Let Peggy's CDs=P J/P =5/3 5P+.5J=.5J + 18, solve for J, P P = 18 CDs that Peggy started with J = 30 CDs that Joe started with. So Joe gave Peggy: 30/2 = 15 CDs.