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We are sometimes encouraged to estimate answers (have a sensible guess).
Estimating gives us an answer that is close to the actual answer and can help us see if an answer is likely to be correct.
We can round to the nearest 10, 100, 1,000, 10,000 etc.
In this activity, we are going to practise rounding to the nearest 10 to estimate some addition questions.
A two-digit number that ends in five or above rounds up to the next ten.
A two-digit number that ends in four or below rounds down to the previous ten.
Example 1
Estimate the answer to the following sum by rounding the numbers to the nearest ten and then adding.
38 + 12
Answer
38 rounds up to 40
12 rounds down to 10
40 + 10 = 50
The actual answer is 50 - a great estimate!
Example 2
Estimate the answer to the following sum by rounding the numbers to the nearest ten and then adding.
64 + 55
Answer
64 rounds down to 60
55 rounds up to 60
60 + 60 = 120
The actual answer is 119 - another great estimate!
Remember, when rounding down we go back to the previous ten - 43 rounds down to 40 (not 30)
Let's have a go at some questions now - good luck!
