Page 121 - ICSE Math 5

Example 14: Add the following integers.
(a) 12 + (–8) (b) 13 + (–15)
Solution: (a) 12 + (–8)

Since the two numbers have different signs and 12 > 8, subtract 8 from 12.
12 – 8 = 4

Here, the greater number 12 is a positive integer, therefore, the sum obtained
will also be positive.
So, 12 + (–8) = +4.
(b) 13 + (–15)

Since the two numbers have different signs and 13 < 15, subtract 13 from 15.
15 – 13 = 2
Here, the greater number 15 is a negative integer, therefore, the sum obtained
will also be negative.

So, 13 + (–15) = –2.

Exercise 8.3

1. Using a number line, write the integer which is:
(a) 5 more than 1. (b) 6 more than –6. (c) 4 less than –4. (d) 5 less than 0.

2. Draw a number line and answer the following.

(a) Which number is reached if we move 3 steps to the right of –15?
(b) Which number is reached if we move 10 steps to the left of –7?

(c) In which direction should we move to reach 0 from –8?
(d) In which direction should we move to reach –1 from –5?

3. Use a number line to add the following integers.
(a) 10 + (–6) (b) (–9) + (–2) (c) 0 + (–6) (d) (–5) + 4 (e) 3 + 5

4. Add the following integers without using a number line.
(a) 12 + (–8) (b) 37 + (–54) (c) (–16) + 5

(d) (–39) + (–56) (e) (–78) + 78 (f) 34 + (–9)
Subtraction of Integers on a Number Line

Subtraction of two positive integers.

When both the subtrahend and the minuend are positive integers, first move to the right of 0 to
reach the subtrahend and then to the left of the subtrahend to find the difference.

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