What is estimation?
Estimation means finding an answer that is close to the exact one, quickly. We do this by rounding the numbers first, then calculating. It helps us check whether an answer looks sensible.
Key idea / 要点
Round each number to the nearest ten, hundred or thousand, then add, subtract, multiply or divide.
Estimating a sum
Round each number, then work with the easy numbers. Estimation is very useful when shopping: round each price to the nearest ringgit to check quickly whether you have enough money. It is faster than finding the exact total, and it is close enough to help.
Worked example / 例题
Estimate 48 + 31. Round to the nearest ten: 48 → 50 and 31 → 30. Now add: 50 + 30 = 80. The exact answer is 79, so 80 is a good estimate.
Remember / 记住
- An estimate is close, not exact.
- Round first, calculate second.
- Use it to check your real answer.