Associative (Grouping) Property of Multiplication

We've been collecting cans of soup for our school's SOUPer Bowl, benefiting a local food pantry.

A generous student brought these this morning:

Perfect timing for today's lesson on the Associative (Grouping) Property of Multiplication!

Sometimes, as in this situation, we need to multiply more than two numbers:

Each box has 2 rows of 5 cans.  There are 2 boxes of soup cans.  How many cans of soup is this?

We could think about it this way:

5 cans in each row x 2 rows x 2 boxes: 5 x 2 x 2

The Associative (Grouping) Property of Multiplication says that the grouping of factors can be changed, and the product will stay the same.

First, we tried grouping (5 x 2) x 2.
(Remember that parenthesis used in math mean "please pay attention to me"; do this part first.)
5 x 2 is 10, and 10 x 2 is 20 cans.

Then we tried 5 x (2 x 2).
2 x 2 is 4, and 4 x 5 is 20 cans.

So, no matter which factors you multiply first, you will always get the same product.


(By the way, you can still send in cans of soup until February 1.  :-) )