Posted by B.B. on Wednesday, June 10, 2009 at 12:11pm.
Here is the original question: Give an estimate for the following expression: 978*66. Is the exact answer going to be greater than or less than the estimate? Here is what I have: I rounded 978 to 1000 and 66 to 70. 1000*70=70,000 the actual answer was 978*66=64,448 so the estimation was greater than the actual answer. Did I do this problem right? I used the rounding technique. Thanks.

Math  MathMate, Wednesday, June 10, 2009 at 12:22pm
The answer is correct.
However, you may want to review your reasoning.
What you said
I rounded 978 to 1000 and 66 to 70. 1000*70=70,000 the actual answer was 978*66=64,448 so the estimation was greater than the actual answer.
seems to tell me that you conclude that you were overestimating after calculating the exact answer, which is not what is intended.
You are expected to determine if you answer is over or underestimating without calculating the exact answer.
Your teacher may prefer to see a reasoning as follows:
"I rounded 978 to 1000 and 66 to 70. 1000*70=70,000. Since I rounded up both multiplicands, the estimation was greater than the actual answer.
Check: 70000>978*66=64,448"
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