Page 63 - Whole Numbers (Addition and Subtraction)

11.3 One number for many

Bennie has to find the sum of the ten to “find the sum”
numbers below. means you have to
He decides to make an estimate by add all the numbers
choosing an easy number that is close to together.
these numbers and multiplying it by 10.

887 734 639 729 901
663 781 809 585 672

Bennie chooses 500 and multiplies it by 10, so his estimate of the
sum is 5 000.

1. Do you think Bennie made a good choice for a single number?
If not, explain why you think 500 is not a good choice.

2. Choose a number that you think is better than 500, and use it
to make your estimate of the sum of the above numbers.

3. Now add up the ten numbers accurately.

4. Was your estimate of the sum better than Bennie’s estimate?
5. Investigate whether the single number 800 would have
produced a better estimate than the number you chose.

6. Which of the following numbers would have been the best
choice for a single number?

600 650 700 750 800

7. Which number would have been a “perfect” choice for a
single number?
8. (a) Choose a single number and use it to estimate the sum of
1 354, 2 007, 1 785, 1 576 and 1 932.

(b) Add the numbers up accurately to check how close your
estimate was.

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