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Rational numbers class 8 important questions

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Question 1
Write the additive inverse of each of the following:

1
$\frac {-1}{9}$
$\frac {-2}{3}$
2
$\frac {-9}{1}$

Answer

(i) 1
Additive inverse = -1
(ii) $\frac {-1}{9}$
Additive inverse = $\frac {1}{9}$
(iii) $\frac {-2}{3}$
Additive inverse = $\frac {2}{3}$
(iv) 2
Additive inverse =-2
(v) -9/1=-9
Additive inverse =9

Question 2
What is the additive identity?

1
-1
0
None of the above

Answer

Additive Identity is same for all Numbers and it is 0

Question 3
True or False Statement

The difference of two rational number is a rational number
Addition of rational numbers is associative
Addition of rational numbers is commutative
Subtraction of rational numbers is not commutative
The addition or subtraction of two rational number is a rational number

Answer

All the statement are true

Question 4
Find the multiplicative inverse of the following.

$\frac {-11}{12}$
$\frac {-10}{9}$
$\frac {1}{2}$
$\frac {-5}{2} \times \frac {-2}{5}$
$\frac {-1}{2} \times \frac {-2}{5}$
- 4

Answer

$\frac {-11}{12}$
Multiplicative inverse => $\frac {-12}{11}$
$\frac {-10}{9}$
Multiplicative inverse = $\frac {-9}{10}$
$\frac {1}{2}$
Multiplicative inverse =2
$\frac {-5}{2} \times \frac {-2}{5} =1$
Multiplicative inverse =1
$\frac {-1}{2} \times \frac {-2}{5} = \frac {1}{5}$
Multiplicative inverse =5
-4
Multiplicative inverse =-1/4

Question 5
Which of these properties hold false for Multiplication of rational numbers?

Associative law
Closure law
Commutative law
Existence of Multiplicative identity
None of the these

Answer

None of these

Question 6
Find the below multiplication

$\frac {-1}{2} \times \frac {9}{10}$
$\frac {-25}{9} \times \frac {1}{3}$
$\frac {7}{24} \times 10$

Answer

$\frac {-1}{2} \times \frac {9}{10}$
$=\frac { -1 \times 9}{2 \times 10} = \frac {-9}{20}$
$\frac {-25}{9} \times \frac {1}{3}$
$= \frac {-25 \times 1}{9 \times 3}= \frac {-25}{27}$
$\frac {7}{24} \times 10$
$= \frac {7 \times 10}{24}= \frac {70}{24}$

Question 7
Find the following

(1/2)^-1
(3)^-1
(-6)^-1
(1/-2)^-1

Answer

Multiplicative inverse of (1/2) =2
Multiplicative inverse of (3) =1/3
Multiplicative inverse of (-6) =-1/6
Multiplicative inverse of (1/-2) =-2

Question 8
The product of two rational number is 2 , if one of the rational number is 1/7 ,what is the value of other?

Answer

Let a be the other number, then
$a \times \frac {1}{7} =2$
Or
$a= 2 \div \frac {1}{7}$
$a=2 \times 7=14$

Question 11
Fill in the blanks
(i) ____   ÷ (-3)= (-4/15)
(ii) The numbers __________ and __________ are their own reciprocals
(iii) The reciprocal of   1   is __________.
(iv)   (1/2)   ÷ (2/3) =__________.
(v) The product of two rational numbers is always a __________.
(vi) The reciprocal of a negative rational number is __________.

Answer

4/5
1 and -1
1
3
Rational Number
Negative rational number

Question 12
Write five rational numbers which are smaller than 5

Answer

Answer:
0,1,2,3,4

Question 13
Find five rational numbers between (1) and 2

Answer

We can write as
$1= \frac {10}{10}$
$2= \frac {20}{10}$
So five rational numbers will be
11/10, 12/10, 13/10,14/10,15/10

Question 14
A car travels a distance 50/3 km in 1/6 hours. What is the speed of the Car?

Answer

Speed = Distance/Time
$s=\frac {50/3}{1/6}= \frac {50}{3} \times \frac {6}{1}=100$ km/hr

Summary

This Rational numbers class 8 important questions is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.

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