Page 120 - ICSE Math 5

Addition of two negative integers

When both the addends are negative integers, first move to the left of 0 to reach the first addend
and then again move to the left of the first addend to find the sum.

Example 12: Add –4 and –3.
Solution: –4 + (–3) = ? (Here, the first integer = –4 and the second integer = –3.)
Move 4 steps to the left of 0 to reach –4.

Since the second integer is also negative, start from –4 and move 3 steps further to
the left of –4 to reach –7.

–10 –9 –8 –7 –6 –5 –4 –3 –2 –1 0 1 2 3 4 5 6 7 8 9 10
So, –4 + (–3) = –7.

Note: When two negative integers are added, addition is performed and the
resultant takes the negative sign.

Addition of Integers without Using a Number Line

(a) When we have two addends or integers with the same signs, their sum is obtained by
simply adding the numbers and writing the same sign in front of the sum obtained.
Example 13: Add the following integers.

(a) 5 + 7 (b) –8 + (–3)
Solution: (a) 5 + 7
Remember
Since both the addends are
positive, simply add them Remember the following while adding
and write ‘+’ sign in front of integers.
nd
st
the sum obtained. 1 2 Operation
Integer Integer
5 + 7 = 12
+ – Subtract
So, 5 + 7 = +12. – + Subtract
(b) –8 + (–3) + + Add
– – Add
Since both the addends
are negative, add the two The answer will carry the sign of the greater
integer.
numbers and write ‘–’ sign
in front of the sum obtained.
8 + 3 = 11

So, –8 + (–3) = –11.
Remember
(b) When we have two integers with different signs, say
one positive and one negative integer, we ignore If there is no sign in
front of a given number,
their signs and subtract the smaller number from the
it means that it is a
greater number. The resulting number so obtained is positive number.
written with the sign of the greater number.

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