1. The problem statement, all variables and given/known data A well insulated cup contains 125 g of water at 23 degrees. How many grams of ice must be added to lower temp to 12? 2. Relevant equations Q = c*m*delta t 3. The attempt at a solution energy needed to lower temp: Q = 4190 J / kg * (-11 degrees) * (.125 kg) = -5760 J Q from ice = - Q from water = 5760 J to find mass of ice needed: 5760 J = Latent heat of ice * mass needed = (3.34 * 10^5 J / kg) * m = .0172 kg = 17.2 g The correct answer is 15 g. What am I doing wrong?