Page 18 - Whole Numbers (Addition and Subtraction)

5. (a) Calculate 850 − 360 and 730 − 270 in any way you prefer.

(b) Check your answers by doing the same calculations in a
different way.

(c) Also check your answers by doing addition.

6. Calculate in any way you prefer, and check each answer by
doing addition.
(a) 780 − 520 (b) 520 − 280
(c) 430 − 160 (d) 760 − 280
(e) 630 − 290 (f) 420 − 340

(g) 480 − 340 (h) 970 − 380

Another way to subtract is to break the numbers down and
work with the parts, then build the answer up.
For example, to calculate 720 − 450 you can think like this:
720 is 700 and 20 and

450 is 400 and 50.
It is easy to subtract 400 from 700 but to subtract 50 from 20
creates a problem.
To make it easier, you can replace 700 + 20 with 600 + 120.
Then you can subtract 50 from 120 and 400 from 600.

So, 720 = 600 + 120 and 450 = 400 + 50.
Hence 720 − 450 = 600 − 400 + 120 − 50

}
= 200 + 70
}
= 270
Instead of the curly signs }
we may use brackets to indicate
the plan to calculate 600 − 400 and 120 − 50 separately:
720 − 450 = (600 − 400) + (120 − 50)

= 200 + 70
= 270

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