For example, evaluate 17520:
Method 1: (175)20 = 8520 = 1,700.
Method 2: 17(520) = 17100 = 1,700.
Notice that by first multiplying 520 to get 100, the calculation
is easy to do in your head.
You can also use the commutative property to rearrange a question:
5214 = 5421 = 2021 = 420