Page 20 - Whole Numbers (Addition and Subtraction)

678 rounded off to the nearest multiple of ten is 680.
678 can also be rounded off to the nearest multiple of
hundred, which is 700.

634 rounded off to the nearest multiple of hundred is 600.
634 rounded off to the nearest multiple of ten is 630.

1. Round off each number to the nearest ten.

(a) 387 (b) 484 (c) 185 (d) 594
(e) 249 (f) 255 (g) 250 (h) 63
2. Round off the numbers in question 1 to the nearest hundred.

3. In each case round off to the nearest ten, then calculate the
sum or difference of the rounded numbers.
(a) 43 + 52 (b) 46 + 52 (c) 46 + 57
(d) 74 − 35 (e) 76 − 35 (f) 76 − 34

4. In each case round off to the nearest hundred, then calculate
the sum or difference of the rounded numbers.
(a) 267 + 466 (b) 932 − 437
(c) 343 + 549 (d) 886 − 278

Rounding off can be used to estimate the answers for calculations.

Example
A traveller has driven 268 kilometres of the 859 kilometres to his
destination. Approximately how far does he still have to drive?

268 and 859 rounded off to the nearest hundred are 300 and 900.
The traveller still has to drive approximately 900 − 300
kilometres, that is 600 kilometres.

Round off to the nearest hundred when you do questions 5 and 6.

5. There are 108 houses in one town, 362 houses in another
town and 269 houses in a third town. Approximately how
many houses are there in the three towns together?

19