What is estimation?
To estimate is to make a smart guess that is close to the real answer. It is quick and helps us check if an answer makes sense. We use estimation every day, like guessing how much our shopping will cost before we reach the counter.
Key idea
A common way to estimate is to round each number to the nearest ten first, then add or count. The answer will be close, not exact.
Estimating a sum
About how much is 38 + 41? Round 38 to 40 and 41 to 40. Then 40 + 40 = 80. So the answer is about 80.
Worked example
A box holds about 30 marbles. About how many are in 3 boxes? Count 30 three times: 30 + 30 + 30 = 90. So about 90 marbles. The real number may be a little more or less, but 90 is a good, close guess.
Remember
- An estimate is close, not exact.
- Round first, then work it out.
- Use it to check your answers.