Why would you use the associative property of multiplication to solve (10*4) * 2

The Associative Property of Multiplication:

Similar examples can illustrate how the associative property works for multiplication.

Example 3: (3 * 5) * 6 = 3 * (5 * 6)

Now which side of the equation is easier for you? Most often, it is 5 * 6 on the right side.

Example 4: 2 * (18 * 10) = (2 * 18) * 10

Here the left side is written differently, yet you can still see how the associative property makes the multiplication on the left side easier.