Page 119 - ICSE Math 5

Example 9: Add 4 and 5.
Solution: 4 + 5 = ? (Here, the first integer = 4 and the second integer = 5.)
Move 4 steps to the right of 0 to reach 4 on the number line and then move 5 steps
further to the right of 4 to reach 9.

–10 –9 –8 –7 –6 –5 –4 –3 –2 –1 0 1 2 3 4 5 6 7 8 9 10
So, 4 + 5 = 9.
Note: When a positive integer is added to a positive integer, the result (sum) is a
positive integer.

Addition of a positive and a negative integer

When the first addend is a positive integer and the second addend is a negative integer, first move
to the right of 0 to reach the first addend and then to the left of the first addend to find the sum.
Example 10: Add 6 and –2.

Solution: 6 + (–2) = ? (Here, the first integer = 6 and the second integer = –2.)
Move 6 steps to the right of 0 to reach 6. Since the second integer is negative,
therefore in order to add the given integers, we start from 6 and move 2 steps back
to the left of 6 to reach 4.

–10 –9 –8 –7 –6 –5 –4 –3 –2 –1 0 1 2 3 4 5 6 7 8 9 10
So, 6 + (–2) = +4.
Note: When a positive integer is added to a negative integer, subtraction is
performed and the resultant integer takes the sign of the larger number.

Addition of a negative and a positive integer

When the first addend is a negative integer and the second addend is a positive integer, first
move to the left of 0 to reach the first addend and then to the right of the first addend to
find the sum.

Example 11: Add –2 and 5.
Solution: –2 + 5 = ? (Here, the first integer= –2 and the second integer = 5.)
Move 2 steps to the left of 0 to reach –2.

Since the second integer is positive, start from –2 and move 5 steps to the right of
–2 to reach 3 in order to add the given integers.

–10 –9 –8 –7 –6 –5 –4 –3 –2 –1 0 1 2 3 4 5 6 7 8 9 10
So, –2 + 5 = 3.
Note: When a negative integer is added to a positive integer, subtraction is
performed and the resultant integer takes the sign of the larger number.

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