You can solve this a couple different ways:
1. You can estimate that 823 is close to 800 and 680 is close to 700. Multiplying these gives you: 800 x 700 = 560,000
2. You can estimate that 823 is close to 825 and 680 is close to 675. Multiplying these gives you: 825 x 675 = 556,875
Remember that estimating does not mean you are supposed to get the actual answer (which in this case is 559,640)--you are just trying to be close. The first estimate above could be done in your head (if you remember that 8 x 7 is 56 and then just add the zeros).
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To estimate the product of 823 and 680, we can round each number to the nearest hundred. 823 is closest to 800 and 680 is closest to 700. When we multiply these rounded numbers (800 x 700), we get 560,000. So, the estimated product of 823 and 680 is around 560,000.
823
680 X 1/8 = 680/8 = 85
The same as 10 sixtyeights; 680
when both factors in a multiplication problem are rounded up to estimate the product, the estimate is an overestimate.
Explain how you know whether an estimate of a product is an overestimate or an underestimate?