Mental Maths Questions and Answers: Rational Numbers | Mental Mathematics for Class 8 PDF Download

Q1: Find the value of:
Ans:

Q2: Find the value of: 
Ans: 

Q3: Find the value of:
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Q4: Find the value of:
Ans: 5/18

Q5: Find the value of:
Ans: 

Q6: Find the value of: 
Ans: 1

Q7: Find the value of: 
Ans: 

Q8: Find the value of:
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Q9: Find the value of:
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Q10: Find the value of:
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Q11: Find the additive inverse of
Ans: 1/8

Q12: Find the additive inverse of
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Q13: Find the multiplicative inverse of
Ans: 24

Q14: Find the multiplicative inverse of
Ans: 

Q15: Find the value of
Ans: 3/10

Q16: The sum of two rational numbers is  if one of them is find the other.
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Q17: What number should be added 9/14 to to get ?
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Q18: What number should be subtracted from  so as to get 3/4?
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Q19: What number should be subtracted from  to get 5/6?
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Q20: What number should be added to  to get 1?
Ans: 1/6

Q21: What number should be added to -1 so as to get 5/7?
Ans: 

Q22: The product of two rational numbers is  If one of the them is  find the other.
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Q23: What number should be multiplied by  to obtain 1/78?
Ans: 

Q24: Find three rational numbers between 2/3 and 3/4.
Ans: 33/48 , 34/48 , 35/48 or any other suitable answer

Q25: Find five rational numbers between 1/4 and 1/3.
Ans: 19/72 , 20/72 , 21/72 , 22/72 , 23/72  or any other suitable answer

Q26: The product of two rational numbers is  If one of them is 14/27, then find the other.
Ans: 

Q27: Find the product of additive inverse and multiplicative inverse of
Ans: -1

Q28: Find the value of
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Q29: Find the value of
Ans: 10

Q30: Divide the sum of 18/5 and  by their difference.
Ans: 47/61

Q31: After reading 2/3 of a book, 20 pages are left. How many pages are there in the book?
Ans: 60 pages

Q32: Amit has ₹1400 with him. He spent 1/2 of his money on notebooks and 1/4 of his money on stationery. How much money is left with him?
Ans: ₹350

Q33: One liter of petrol costs ₹ 175. What is the cost of  litres of petrol?
Ans: ₹ 560

Q34: If 6 shirts of equal sizes can be made out of 15 meter of cloth, how much cloth is needed for making one shirt?
Ans: 2.5 m

Q35:  of long rope is cut into 11 equal pieces. What is the length of each piece?
Ans: 0.5m or 50cm

Q36: The product of two fractions is  If one of the fraction is 48/7 , find the other.
Ans: 

Q37: At a football match 3/7 of the spectators were in covered place while remaining 12000 were in open. Find the total number of spectators.
Ans: 21000

Q38: A drum full of sugar weighs  kilogram. If the empty drum weighs 72/5 kilogram, find the weight of sugar.
Ans: 16 kilogram

Q39: An aeroplane covers 780 kilometers in an hour. How much distance will it cover in  hours?
Ans: 1950 kilometre

Q40: In a school, 5/8 of the students are girls. If there are 240 boys, find the number of girls in the school.
Ans: 400 girls

For detail explanation of solutions refer to the videos provided