Page 23 - Whole Numbers (Addition and Subtraction)

Some people think of movements on a number line to help them
to keep track of their thinking when they use the above method
of subtraction:
568 734

0 100 200 300 400 500 600 700 800 900

500 568 600 700 734

B. The break down and build up method

In a case such as 786 − 523, the break down and build up method
is quite easy:
786 = 700 + 80 + 6 or 700 and 80 and 6.
523 = 500 + 20 + 3 or 500 and 20 and 3.

500 can be taken from 700 to give 200: 700 − 500 = 200
20 can be taken from 80 to give 60: 80 − 20 = 60
3 can be taken from 6 to give 3: 6 − 3 = 3
Hence 786 − 523 = 200 + 60 + 3, which is 263.

5. Use the break down and build up method to calculate each of the
following.

(a) 937 − 624 (b) 876 − 445
(c) 348 − 33 (d) 987 − 352

6. Do the calculations in question 5 with the filling-up method.
Then compare the answers that you got with the two methods
to check whether you worked correctly.
7. Try to calculate 924 − 637 using the break down and build up
method.

8. Write each of the following as a single number.
(a) 800 + 40 + 3 (b) 700 + 130 + 13

(c) 600 + 70 + 19 (d) 400 + 260 + 39

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