A baby weighs 7 1/8 pounds then after four months it now weighs 15 2/3, how much did the baby gain?
current weight - old weight = gained weight
\(15\frac23-7\frac18=g \\~\\ = 15\frac{2*8}{3*8}-7\frac{1*3}{8*3} \\~\\ = 15\frac{16}{24}-7\frac{3}{24} \\~\\ = 8\frac{13}{24}\text{ pounds}\)