Use friendly tens
For a quick estimate, move a number to the nearest ten. The ones digit helps you decide which ten is closer.
Class 2 Maths · Chapter 1 · Topic 1-4
Estimate Numbers
An estimate is a sensible answer that is close to the exact amount. Use friendly tens, halfway points and what you already know to make a good estimate.
30CHALLENGES
Learn · notice · estimate
How to make a smart estimate
Close is useful. An estimate does not need to be exact.
Find the halfway point
Numbers ending in 1–4 are closer to the lower ten. Numbers ending in 5–9 are closer to the next ten. At 5, round up.
Estimate before calculating
Replace numbers with nearby friendly tens, then add or subtract. Ask if your estimate makes sense for the story.
A number line can help
Where does 36 belong?
36 is between 30 and 40. The halfway number is 35. Since 36 is past halfway, it is closer to 40.
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Example · nearest ten
Estimate 42 to the nearest ten.
42 is 2 away from 40 and 8 away from 50, so 40 is the closer ten.
42→about 40
Example · estimate a sum
About how much is 28 + 41?
28 is about 30. 41 is about 40. Add the friendly tens: 30 + 40 = 70.
28 + 41→30 + 40 ≈ 70
Read the question
Does it ask for an estimate, an exact answer, or a number close to a given amount?
Choose a helpful ten
Use the closest ten, a group of ten, or a friendly number that makes the calculation easier.
Check if it makes sense
An estimate should be close. For addition it should be near the total; for subtraction, near the difference.
Remember: Estimate means “about how many?” If a question asks “exactly how many?”, count or calculate the exact answer instead.
30 ways to practise
Estimate, choose and explain
Check each answer to reveal a short solution.
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Your estimate score is ready when you are!
Try all 30 questions. You can change an answer and check it again.