Compatible numbers - Math Central

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Question from jeff, a parent:

what exactly are compatible numbers,
math problem is:
Estimate the total weight of 2 boxes that weigh 9.4 pounds and 62,6 pounds
using rounding and compatible numbers. Which estimate is closer to the actual weight and why?

Hi Jeff,

Compatible numbers are not well defined things. The idea with compatible numbers is to replace the numbers in the problem with numbers that are approximately the same and yet the calculations are easy. In this problem what I think is expected is to replace 9.4 with 10 and 62.6 with 60 giving an approximate sum of 10 + 60 = 70.

Rounding has a more precise definition. If you are rounding to an integer then 9.4 rounds to 9 and 62.6 to 67. This gives an approximate sum of 9 + 63 = 72.

Harley

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