Estimate, make a reasonable guess, check the guess, and revise. Using the example in number 6, if you were told that Sarah had a large number of coins that added up to $82.00, you could at least say...

Estimate, make a reasonable guess, check the guess, and revise. Using the example in number 6, if you were told that Sarah had a large number of coins that added up to $82.00, you could at least say that the total was no more than 8,200 (the number of coins if they were all pennies) and no less than 328 (the number of coins if they were all quarters).