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Round to the nearest hundred
3920 rounds to 3900 and 1731 rounds to 1700. Subtracting the rounded values is quick and gives a close estimate.
3920 − 1731 ≈ 3900 − 1700 = 2200
Worked example
The exact difference is 2,189, so 2,200 is an excellent estimate.
Why place-value choice matters
Rounding to the nearest thousand would give 4,000 − 2,000 = 2,000, which is useful but less precise. Hundreds give a better estimate without making the arithmetic difficult.
Common mistakes
- Rounding 1731 to 1800 when using nearest hundred.
- Forgetting that subtraction order matters.
- Adding the rounded numbers instead of subtracting them.
Frequently asked questions
What is the best estimate for 3920 − 1731?
About 2,200.
What is the exact answer?
2,189.
Can I estimate with thousands?
Yes, but 2,000 is a rougher estimate.