what strategy should I use to workout 45 times 8 mentally?
Have you checked out "Number Talks"? It's interesting to see how many different ways students can come up with an answer for 45 times 8 mentally. Here's an example (This is what I do):
45 times 8 is equivalent to (40 * 8) + (5 *8) = 320 + 40 = 360.
Some students do 50 times 8, which is 400, then take away 5 times 8, because we added too many 8's. So 400 minus 40 gives us 360.
Using the standard algorithm is difficult to perform mentally, since you have to remember your "carrying" values.
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I agree with all of the great suggestions Josh gave above!
I also really love using the doubling and halving strategy when one of the numbers end in a 5. I could double the 45 to 90 and half the 8 to 4 and know 90x4=360 much easier and that it has to be equivalent because of what is happening to the area when I do that!
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