FACTS  AND  FORMULAE  FOR  AVERAGE QUESTIONS

 

 

1. Average =Sum of observationsNo. of observations

2. Suppose a man covers a certain distance x kmph and an equal distance at y kmph. Then, the average speed during the whole journey is2xyx+yKmph

Q:

An oil refinery buys oil at Rs 3600 per barrel. There is 10% wastage. If the refinery wants to earn 5% profit then at what price should it sell including 8% tax on selling price? (in Rs per barrel)

A) 3674 B) 3711
C) 4219 D) 4536
 
Answer & Explanation Answer: D) 4536

Explanation:
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Q:

The average weight of 50 boys in a class is 45 Kg. When one boy leaves the class, the average reduces by 100g. Find the weight of the boy who left the class.

A) 50 Kg B) 50.8 Kg
C) 49 Kg D) 49.9 Kg
 
Answer & Explanation Answer: D) 49.9 Kg

Explanation:

Total weight of 50 boys = 45 X 50 = 2250

Average weight of 49 boys = 44.9

Total weight of 49 boys = 44.9 X 49 = 2200.1

Weight of boy who left the class=2250–2200.1=49.9

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Q:

After replacing an old member by a new member, it was found that the average age of five members of a club is the same as it was 3 years ago. The difference between the ages of the replaced and the new members?

A) 16 years B) 15 years
C) 14 years D) 13 years
 
Answer & Explanation Answer: B) 15 years

Explanation:

Let avg ages of 5 members at present is G

And age of new member is m and an older is n

Required = (5G + m - n)/5 = G - 3

m - n = 15 years

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Q:

The average weight of L, M and N is 93 kg. If the average weight of L and M be 89 kg and that of M and N be 96.5 kg, then the weight (in kg) of M is ________.

A) 92 B) 86
C) 101 D) 95
 
Answer & Explanation Answer: A) 92

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Q:

A student's average marks in five subjects is 82. If the average marks of first two subject is 86.5 and the average marks of last two subjects is 84. Find the marks of third subject?

A) 69 B) 67
C) 71 D) 73
 
Answer & Explanation Answer: A) 69

Explanation:

The total marks of all 5 subjects = 82 x 5 = 410

Total marks of 1st two subjects = 86.5 x 2 = 173

Total marks of last two subjects = 84 x 2 = 168

Now, marks in 3rd subject = 410 - (173 + 168) = 410 - 341 = 69.

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Q:

Average age of 20 students is 21 years. 2 students leave the group and 1 new student joins the group. The average now becomes 20 years. If age of one of the student who left the group is 26 years and the one who joined is 20 years, then what is the age (in years) of the other student who left the group?

A) 20 B) 14
C) 22 D) 16
 
Answer & Explanation Answer: B) 14

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Q:

Due to a price hike of 20% , 4 kg less sugar is available for Rs. 120 . What is the initial price per kg of sugar ?

A) Rs. 5 Kg B) Rs. 4 Kg
C) Rs. 6 Kg D) Rs. 5.5 Kg
 
Answer & Explanation Answer: A) Rs. 5 Kg

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Q:

What is the average of first 7 multiples of 7?

A) 7 B) 14
C) 28 D) 21
 
Answer & Explanation Answer: C) 28

Explanation:
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