Page 73 - Maths Skills - 7
P. 73
Rational Numbers 71
2. Subtract.
17 − 8 3 − 19 13 4 −17
(i) from (ii) − 7 from 21 (iii) from (iv) from 0
51 17 17 15 27
3. Fill in the blanks.
− 4 3 15 − 7 − 5
(i) − = ..... (ii) ...... + = 4 (iii) + ..... = 3 (iv) + ..... = −1
13 26 23 9 14
4. What number should be added to – 1 so as to get 9
7?
5. Subtract the sum of –23 and 17 from the sum of 33 and 18 .
11 7 5 4
6. The sum of two rational numbers is – 7. If one of the numbers is –15 , find the other number.
9 1
7. Sohail and Ruby go for a morning walk in the park everyday. Sohail covers 2 km and Ruby covers
3 3
2 km. Who covered a greater distance and by how much?
5
8. Ramit, Sumi and Laila were playing a game which had 12 chances for each in total. Ramit won 5 times,
2
Sumi lost 5 times and Laila’s score was . Who won in the game?
3
1
9. A hot air balloon ascended in air and reached a height of 11 m from sea level and descended by
1 2
7 m. Find its final height above the sea level.
3
Multiplication of Rational Numbers
The product of two rational numbers is obtained just like the product of two fractions.
Productof numerators Fact-o-meter
We know that the product of two fractions = .
Productofdenominators
� (+ve) × (+ve) = +ve
The same rule holds true for the rational numbers also. � (–ve) × (–ve) = +ve
Productof numerators � (+ve) × (–ve) = –ve
Thus, the product of two rational numbers = Productofdenominators . � (–ve) × (+ve) = –ve
p r p r pr×
In general, if q and s are any two rational numbers, then their product is q × s = qs .
×
9 − 5 9 ×−( 5) − 45 − 4 8 −×48 − 32
For example; (i) × = = (ii) × = =
7 6 76× 42 11 9 11 × 9 99
Reciprocal or Multiplicative Inverse of a Rational Number
For every non-zero rational number, there exists a rational number such that their product is equal to one.
p r p r r p p
In general, if and are any two rational numbers such that × == ×1 , then is called the multiplicative
q s q s s q q
r
inverse or reciprocal of and vice versa.
s
19 8 19 8
For example, the reciprocal of is . [Q × = ] 1
8 19 8 19
