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Round numbers to the nearest ten, hundred, thousand or whole number, and use rounding to estimate answers quickly.
The real crowd at the stadium might have been 38,652 people. Nobody needs every digit — "about 40,000" is easier to say and remember. That is rounding, and it also helps you check your sums in the market.
Rounding means replacing a number with a nearby, simpler number.
47 lies between 40 and 50. It is 3 away from 50 but 7 away from 40, so 47 rounded to the nearest ten is 50.
When a number is exactly halfway, like 45, we round up to 50.
🔑 Key idea: Round to whichever value is nearer. Halfway rounds up.
Look at the digit just after the place you are rounding to. If it is 5 or more, round up; if it is 4 or less, round down.
3,462 to the nearest hundred: the digit after the hundreds is 6, so round up to 3,500. The places after become zeros, so the number stays about the same size.
Decimals work the same way: 12.68 to the nearest whole number is 13 (the tenths digit is 6), and to 1 decimal place it is 12.7.
🔑 Key idea: 5 or more → round up. 4 or less → round down.
An estimate is a rough answer found by rounding first. It is quick to do in your head.
₦387 + ₦512 ≈ ₦400 + ₦500 = ₦900. The exact total is ₦899 — very close!
Estimating helps you spot mistakes: if your calculator says ₦8,990, you know something is wrong.
🔑 Key idea: Round, then calculate — use estimates to check answers.
A farmer harvested 11,444 tubers of yam. Round this number to the nearest ten.
Step 1: Find the two nearest multiples
11,444 is between 11,440 and 11,450.
Step 2: Look at the deciding digit
The digit after the tens place is 4.
4 is less than 5, so round DOWN.
Step 3: Answer
11,444 ≈ 11,440
Why? Rounding keeps the number the same size — the dropped places become zeros.
Answer: 11,440
Ready to check you've got it? Scroll up and work through the lesson: the interactive visuals, practice questions and mastery check are all there.