For example, evaluate 17*5*20: Method 1: (17*5)*20 = 85*20 = 1,700. Method 2: 17*(5*20) = 17*100 = 1,700. Notice that by first multiplying 5*20 to get 100, the calculation is easy to do in your head. You can also use the commutative property to rearrange a question: 5*21*4 = 5*4*21 = 20*21 = 420
