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| Math Central | Quandaries & Queries |
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Question from monica, a parent: the questions in the homework says change the order or group the addends so that you can add mentally ,find the sum and tell which property you used |
Hi Monica,
I want to consider $15 + 9 + 15.$ I look for two of the three numbers that I can easily add. I know that $15 + 15 = 30$ so in my mind I think of $15 + 9 + 15$ as $15 + 15$ and then add $9.$ Thus $15 + 9 + 15$ is $15 + 15 = 30$ plus $9$ more which is $39.$ The idea is to do this mentally without the need to write it down.
Let's try another, $250 + 35 + 150.$ Here I see that $250 + 150 = 400$ so $250 + 35 + 150 = 400 + 35 = 435.$
I hope this helps,
Penny
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