You don't always need the exact answer. You need one close enough to plan with, and you need it fast.
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Students will estimate sums and differences by rounding each number to a chosen place value, then working with the rounded numbers instead of the real ones. The skill is deciding which place value to round to and trusting the estimate as a check.
Rounding looks at one digit only, the one immediately to the right of the place value being rounded. Under 5 rounds down, 5 or more rounds up. The same rule works on tens, hundreds, thousands or dollars.
A rounded total tells you whether a real total is even in the right neighborhood. The fund-raising committee needed about $1,400 before Mark added a single real price, and the grocery total was checked the same way after the fact.
Rounding several numbers to different place values in the same sum, rather than all to the same one, throws the estimate off. Watch for a student who rounds one price to the nearest ten and another to the nearest hundred in the same problem.
Hand him a real register receipt or a phone bill and ask him to round every line to the nearest dollar before checking the total. It's the same skill as the grocery example, on paper he can hold.
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Before You Start
The words this lesson uses. Tap a card to see what it means, then come back to them whenever a question uses one.
Part One
Questions about the story you just read. Pick your answer straight off, or press Find it in the story if you would rather hunt for the sentence first.
Part Two
The word cards are at the top of this page. Look back at them as often as you need, then answer.