Practice Estimation
Estimation uses rounded numbers to find an approximate result before or after an exact calculation.
It helps you spot errors in prices, measurements and statistics.
Exercises with solutions
To estimate, round the numbers sensibly and calculate in your head. The result is not exact but shows the right order of magnitude. That lets you judge whether a calculated answer can be correct at all.
Exercise 1
Estimate 198 + 403.
Show solution and working
about 600
Round 198 to 200 and 403 to 400. 200 + 400 = 600. The exact answer is 601.
Exercise 2
Estimate 6 · 19.
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about 120
Round 19 to 20. 6 · 20 = 120. The exact answer is 114.
Exercise 3
Is 302 − 98 = 4 a plausible answer?
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No, the estimate gives about 200
Round 302 to 300 and 98 to 100. 300 − 100 = 200. So 4 cannot be right; the correct answer is 204.
Exercise 4
Estimate 7 · 31.
Show solution and working
about 210
Round 31 to 30. 7 · 30 = 210. The exact answer is 217.
Common mistake
Taking the estimate for the exact answer. The estimate is only a check. Round both numbers to a value you can calculate easily in your head.
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