When we multiply we can break apart numbers to "start with" what we know. 9 out of 10 fourth graders agree that the 10 times table is easy as pie! So why not start there?! Our Good Friend 10 multiplication strategy is an efficient way to work. Try one out yourself!
7 X 17
Gee, I am no good at the 17 times table...
but I know:
7 X 10 = 70!
If I take away 10 from 17, I am left with 7. I just need 7 more sevens!
7 X 7 = 49
I know my square numbers.
So now I need to do easy addition to get my final answer.
100 + 49 = 149
(7 X 10) + (7 X 7) is the same as 7 X 17
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