Page 72 - Maths Skills - 7

70 Maths

Thus, subtracting a rational number means adding its additive inverse.

p r p  r 
∴ − = + additiveinverse of  .

q s q   s
Let’s learn more through examples.

Let’s Attempt

− − 5 1
Example 1: Subtract from . Example 2: What number should be added to − 3 ,
3 4 15 5
5
Solution: The additive inverse of − 5 is . so as to get 8 ?
3 3 − 3
−1  5 −1 5 Solution: The given number is .
− 
∴ −   = + 5
4  3  4 3 The required number is
−+320 17 15 − 3  1 5 3 75 24+ 99
= = −  = + = = .
12 12 8   5   8 5 40 40

− 9
Example 3: The sum of two rational numbers is – 4. If one number is , find the other.
7

Solution: The sum of the two rational numbers is – 4 and one number is − 9 .
7
+
 −  9 − 4 9 − 28 9 −19
∴ The other number =− −4   = 1 + 7 = 7 = 7

 7
1 1 1
Example 4: On a fruit stall, are bananas, are oranges and are kiwis. The remaining are watermelons.
4 5 3
What part of the stall has watermelons?
1 1 1
Solution: Quantity of bananas = , Quantity of oranges = , Quantity of kiwis =
4 5 3
1 1 1 15 12 20+ + 47
Total quantity = ++ = =
4 5 3 60 60

47 60 47− 13
Quantity of watermelons = 1− = =
60 60 60

13 .
Hence, the required fraction is
60

Exercise 4.4

1. Subtract.

6 3 − 8 −13 − 9 3 7 1 − 5
(i) − (ii) − (iii) 0 − (iv) − (v) −
7 7 9 18 13 8 8 3 6