Rounding and estimating to check answers
A quick rounded estimate is your safety net — if your calculator answer is wildly different, you know something went wrong before you hand in the work.
Part of your national curriculum
- Number: Round numbers and measures to an appropriate degree of accuracy and use approximation to check answers
Lesson overview
What you'll learn in this lesson
Round numbers and measures to an appropriate degree of accuracy and use approximation to check answers
Key learning points
- • Rounding rules
- • Worked example
- • Using estimates to check
This lesson at a glance
- 22 minutes
- 16 parts to scroll through
- 3 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 16
Visual introductionPicture this
Rounding and estimating to check answers
A quick rounded estimate is your safety net — if your calculator answer is wildly different, you know something went wrong before you hand in the work.
In a nutshell
Round numbers and measures to an appropriate degree of accuracy and use approximation to check answers
Learning cycle
Part 2 of 16
Learning cycle 1 of 2
Part 1 · Rounding rules
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 16
Learn
Rounding rules
To round to a given place value, look at the next digit: 5 or more rounds up, below 5 rounds down. 47.3 rounds to 47 (nearest whole), and 462 rounds to 500 (nearest hundred).
Reset break
Part 4 of 16
Pause
That's sitting 1 of 4 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 16
Learn
Worked example
Estimate 38 × 21 by rounding to the nearest 10: 40 × 20 = 800. The actual answer, 798, is very close, confirming the calculation is sensible.
Quick check
Part 6 of 16
Quick check
Part 7 of 16
Reset break
Part 8 of 16
Pause
That's sitting 2 of 4 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 16
Learning cycle 2 of 2
Part 2 · Using estimates to check
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 16
Learn
Using estimates to check
If a bill calculation gives £1,245 for 3 items at about £40 each, the estimate 3 × 40 = £120 shows something has gone very wrong — you would recheck the working.
Quick check
Part 11 of 16
Reset break
Part 12 of 16
Pause
That's sitting 3 of 4 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 13 of 16
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 14 of 16
Game · Recall cards
Round 462 to the nearest hundred.
Card 1 of 4
Mastery quiz
Part 15 of 16
Marked quiz
End of lesson quiz: Rounding and estimating to check answers
4 questions, marked with the reasoning shown. No timer.
1. Round 462 to the nearest hundred.
2. Estimate 38 × 21 by rounding to the nearest 10.
3. Why use estimation before an exact calculation?
4. 0.004072 to 2 significant figures is
Lesson round-up
Part 16 of 16
Lesson round-up
Ready when you are
Quiz score
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Luna: 0 out of 3 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 16 · Watch & discover
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Round numbers and measures to an appropriate degree of accuracy and use approximation to check answers