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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. 1
  2. $\frac {-1}{9}$
  3. $ \frac {-2}{3}$
  4. 2
  5. $\frac {-9}{1}$

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
  2. -1
  3. 0
  4. None of the above

Answer

Additive Identity is same for all Numbers and it is 0


Question 3
True or False Statement
  1. The difference of two rational number is a rational number
  2. Addition of rational numbers is associative
  3. Addition of rational numbers is commutative
  4. Subtraction of rational numbers is not commutative
  5. 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.
  1. $ \frac {-11}{12}$
  2. $ \frac {-10}{9}$
  3. $ \frac {1}{2}$
  4. $\frac {-5}{2} \times \frac {-2}{5}$
  5. $\frac {-1}{2} \times \frac {-2}{5}$
  6. - 4

Answer

  1. $ \frac {-11}{12}$
    Multiplicative inverse =>$ \frac {-12}{11}$
  2. $ \frac {-10}{9}$
    Multiplicative inverse =$ \frac {-9}{10}$
  3. $ \frac {1}{2}$
    Multiplicative inverse =2
  4. $\frac {-5}{2} \times \frac {-2}{5} =1$
    Multiplicative inverse =1
  5. $\frac {-1}{2} \times \frac {-2}{5} = \frac {1}{5}$
    Multiplicative inverse =5
  6. -4
    Multiplicative inverse =-1/4



Question 5
Which of these properties hold false for Multiplication of rational numbers?
  1.  Associative law
  2. Closure law
  3. Commutative law
  4. Existence of Multiplicative identity
  5. None of the these

Answer

None of these


Question 6
Find the below multiplication
  1. $ \frac {-1}{2} \times \frac {9}{10}$
  2. $ \frac {-25}{9} \times \frac {1}{3}$
  3. $\frac {7}{24} \times 10$

Answer

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


Question 7
Find the following
  1.  (1/2)-1
  2. (3)-1
  3. (-6)-1
  4. (1/-2)-1

Answer

  1. Multiplicative inverse of (1/2)   =2
  2. Multiplicative inverse of (3)   =1/3
  3. Multiplicative inverse of (-6)   =-1/6
  4. 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

  1. 4/5
  2. 1 and -1
  3.  1
  4. 3
  5. Rational Number
  6. 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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