Estimating: rounding to the nearest 10 or 100 to add or subtract in your head. Your child uses estimates to check if an answer makes sense, and to answer when close is enough.
Round each number, then add or subtract the rounded numbers: 392 − 148 is about 400 − 100 = 300. An exact answer far from the estimate needs a second look.
estimatea close answer, not an exact one
roundchange to the nearest 10 or 100
reasonableclose enough to the estimate to make sense
abouta word that often means estimate
Watch for: Rounding 148 to 200 by looking at the 8: for hundreds, the tens digit decides. Working out the exact answer and skipping the estimate the sheet asks for. Calling an answer wrong just because it doesn't equal the estimate: close is reasonable.
At home: At the store, round a few prices to the nearest dollar and estimate the total before checkout. Then see how close you got.
Sample sheet and answer key
Luna's Space Adventure
Grade 3 · Estimating sums and differences · 3.NOS.D.6
NameDate
Astronaut Luna is exploring a far-off corner of space. Solve each problem to help Luna's mission go smoothly!
Round, then estimate
Round each number to the nearest 100, then add or subtract.
Estimate to the nearest 100, then circle yes or no.
1
A box holds 900 space snacks. Orion packs 473 space snacks and Max packs 159 more. Will they all fit?
Estimate: 700500 + 200 = 700
yesno
2
Nova has 414 star stickers and gives 344 of them to Orion. Does Nova still have at least 300?
Estimate: 100400 − 300 = 100
yesno
Answer key
New problems every time, three levels (gentle, core and stretch), themes to pick from, a second page if you want one. Each sheet comes with an answer key and a one-page guide for grown-ups.
