Page 48 - ICSE Math 6

Example 16: Subtract the following.
(a) +9 from +19 (b) –9 from +19 (c) +9 from –19 (d) –9 from –19
Solution: (a) +19 – (+9) = +19 – 9 = +10 (b) +19 – (–9) = +19 + 9 = +28

(c) –19 – (+9) = –19 – 9 = –28 (d) –19 – (–9) = –19 + 9 = –10
Example 17: Evaluate.
(a) (+50) – (–21) + (+10) + (–18) (b) (+54) + (–75) – (–26) – (+30)

Solution: (a) (+50) – (–21) + (+10) + (–18) = +50 + 21 + 10 + (–18)
= +81 –18 = +63
(b) (+54) + (–75) – (–26) – (+30) = (+54) + (–75) + 26 – 30

= –21 – 4 = –25

Subtraction of integers on a number line

To subtract a positive integer, say a, from a given integer on the number line, we move a units to the
left of the given integer on the number line. For example, to subtract +2 from –6, we move 2 units to
the left of –6 on the number line.

–8 –7 –6 –5 –4 –3 –2 –1 0 1
\ (–6) – (+2) = –8 Try These

To subtract a negative integer, say –b, from a given 1. Use the number line to find the value of:
integer on the number line, we move b units to the (a) (–4) – (–4) (b) (+7) – (+3)
right of the given integer on the number line. For 2. To find the value of (–2) – (+3) on the number line,
one should move:
example, to subtract –2 from +6, we move 2 units to (i) 2 units to the right of 3
the right of +6 on the number line. (ii) 2 units to the left of 3
(iii) 3 units to the right of –2
(iv) 3 units to the left of –2
–1 0 1 2 3 4 5 6 7 8
\ (+6) – (–2) = +8
Example 18: Subtract –2 from 11 on the number line.

Solution: We have 11 – (–2) = 11 + 2
Move 11 units to the right of 0 to reach 11 and then move 2 units to the right of 11 to
reach 13.

–1 0 1 2 3 4 5 6 7 8 9 10 11 12 13

\ 11 – (–2) = 11 + 2 = 13

EXERCISE 3.2

1. Add the following.
(a) –75 and –65 (b) –75 and +65 (c) –105 and –256

(d) –105 and +256 (e) 624 and –86 (f) –620 and 0

32