Question

Compute $ 9 + \left( { - 7} \right) $

Answer 1

Hint: Given a sum of two integers, sum because it has a ‘+’ sign. One is 9, a positive integer and another is -7, a negative integer. Sum of a positive integer and negative integer is not exactly a sum, rather a difference. So subtract the smaller number from the larger number and put the sign of the larger number for the result. The result will have the sign of the larger number.

Complete step-by-step answer:
We are given to compute $ 9 + \left( { - 7} \right) $ .
The numbers 9 and -7 are integers. Integers are numbers which can be written without fractional components. Integers can be either negative or positive. Fractions are not integers. For example 2, -4, -5, 7 are integers whereas 7.5, $ \dfrac{2}{3} $ , $ \sqrt 5 $ are not integers.
Here 9 is a positive integer and -7 is a negative integer. Sum of a positive and negative integer is a difference.
So $ 9 + \left( { - 7} \right) $ can also be written as $ 9 - 7 $ .
In a subtraction, we always subtract the smaller number from the bigger number. Here 7 is smaller than 9. So subtract 7 from 9 and the result will have the sign of the larger number. 9 is the larger one and it has a positive sign (9 is positive). So the result will have a positive sign.
Therefore, $ 9 - 7 = + 2 $
The value of $ 9 + \left( { - 7} \right) $ is 2.
So, the correct answer is “2”.

Note: Adding two positive integers will result in a positive integer. Sum of two negative integers is a negative integer and the integers must be added but the result will have a negative sign. Sum becomes a difference only when we add unlike integers.