408
First, 7 x 24 = (7 x 20) + (7 x 4) = 140 + 28 = 168. Then, 17x24 = (10 x 24) + (7 x 24) = 240 + 168 = 408. ----Alternately, take a factor of 3 away from 24, so it becomes 8, and give it to 17, so it becomes 51. Then, 24(17) = 8(51) = 8(50 + 1) = 400 + 8 = 408.