In the first problem, we can round the price $11.95 up to $12, which is just five cents more than the real price. Then, to find the price of four items, we can go 4 x $12 = $48, which is 4 x 5 cents too much... so the real total is $47.80. The question is asking for change from $50, which is now easy to figure out by adding up (mental math).
In the second problem, we find out how many $0.80 cookies you can get with $20. It turns out, instead of using division, it's easier to use multiplication and mental math to find the answer.
This lesson is intended for 4th grade in my Math Mammoth curriculum, but it's also good for older students who don't know these techniques/strategies.
Tagged under: mental math,estimation,4th grade,math,multiplication,money,word problem
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