Average Questions and Answers

Exercise


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Q 1

One adult and 10 children are on an elevator. If the adult's weight is 4 times the average (arithmetic mean) weight of the children, the adult's weight is what fraction of the 


A)  

1/11

B)  

2/7

C)  

4/11

D)  

2/5


Correct Option - B

Explanation

Let the average weight of the 10 children be x.

Adult's weight = 4x

Total weight of 11 people

= 10x+4x

= 14x

4x/14x = 2/7

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Q 2

The average height of a class of 30 students is 166 cm. The average height of the girls in the class is 158 cm and the average height of the boys is 170 cm. Find the number of 


A)  

10

B)  

20

C)  

15

D)  

18


Correct Option - B

Explanation

Let the number of boys be x.

170x + 158*(30-x) = 166*30

Solving, x = 20

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Q 3

The average age of 10 members of a committee is the same as it was 4 years ago, because an old member has been replaced by a young member. Find how much younger is 


A)  

10

B)  

20

C)  

30

D)  

40


Correct Option - D

Explanation

The sum of the ages of the 10 members after 4 years increases by 40.

Since the average remains the same, the sum should remain the same.

Hence, the new member is 40 years younger than the replaced member.


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Q 4

The average mark of a class in a mathematics exam is 65. The sum of the marks of all students is 2210. How many students are there in the class?


A)  

34

B)  

44

C)  

32

D)  

42


Correct Option - A

Explanation

Number of Students

= Sum/Average

= 2210/65

= 34

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Q 5

Find the average of the first 50 whole numbers.


A)  

24

B)  

24.5

C)  

25

D)  

25.5


Correct Option - B

Explanation

Sum of the first 50 whole numbers 

= 0+1+2+….+48+49 

= 49*50/2 

Avg = Sum/50 = 49/2 = 24.5

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Q 6

If the average of x and y is 30 and the average of y and z is 20, find x-z.


A)  

10

B)  

15

C)  

30

D)  

20


Correct Option - D

Explanation

(x+y)/2 = 30

x+y=60

(y+z)/2 = 20

y+z=40

x-z = (x+y)-(y+z)

  = 20 

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Q 7

Find the average of the first ten multiples of 3.


A)  

30

B)  

15

C)  

18

D)  

16.5


Correct Option - D

Explanation

Sum of the first 10 multiples of 3 

= 3+6+9+…+30 

= 3*(1+2+..+10) 

= 3*(10*11/2) 

= 165

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