You are given the
mass of hydrate which is 10.24g and the mass of anhydrate which is 8.74g. Hydrate
means that it contains water and anhydrate means the substance has lost water
during the process. So you just subtract them, 10.24g – 8.74g = 1.5g of water
is lost. Percent hydration is equal to one subtracted to the mass of anhydrate
divided by the mass of hydrate multiplied by 100. So we have, [1-(8.74g/10.24g)]
*100 = 14.65% or 15%. Your answers are correct.