Average

1. The average of first five even numbers are

A. 6

B. 9

C. 12

D. 15

Ans: A

Explanation:

\text {First five even numbers are = 2, 4, 6, 8, 10}

 

\text {Average} = \frac{2+4+6+8+10}{5} = \frac{30}{5} = 6

 

 

2. Three students got 60,72, and 66 marks in an exam respectively. Find the average.
A. 52

B. 58

C. 60

D. 66

Ans: D
Explanation:

\text {sum of observations} = 60 + 72 + 66 = 198

 

\text {Number of observations} = 3

 

\text {Average} = \frac{198}{3} = 66

 

 

3. The average cost of 5 mangoes is Rs.6. In them average of 3 mangoes is Rs.4.

find the average cost of remaining.

A. 5

B. 6

C. 9

D. 10

Ans: C

Explanation:

\text {Total cost of 5 mangoes} = 5 \times 6 = 30

 

\text {Total cost of 3 mangoes} = 3 \times 4 = 12

 

\text {Total cost of 2 mangoes} = 30 - 12 = 18

 

\text {Average of 2 mangoes} = \frac{18}{2} = 9

 

 

4. Average age of 45 students is 12 years. Find the total age of the students.

A. 450

B. 540

C. 620

D. 680

Ans: B

Explanation:

\text {Average age of students = 12 years}

 

\text {Number of students = 45}

 

\text {Total age of students} = 12 \times 45 = 540

 

 

5. Find the average of first 20 multiples of 7.

A. 73.5

B. 70.5

C. 60.5

D. 75.5

Ans: A

Explanation:

\text {Required average} = \frac{7\left ( 1+2+3+...+20 \right )}{20} = \frac{1470}{20} = 73.5

 

 

6. The average of four consecutive even numbers is 27. Find the Largest of these numbers.

A. 26

B. 28

C. 30

D. 32

Ans: C

Explanation:

\text {Let the numbers be }x, x+2, x+\text{4 and }x+6

 

\frac{x+ \left ( x+2 \right )+\left ( x+4 \right ) + \left ( x+6 \right )}{4} = 27

 

 

\frac{4x+12}{4} = 27

 

 

x + 3 = 27

 

x = 24

 

\therefore \text{The largest number} = \left ( x+6 \right ) = 24 + 6 = 30

 

 

7. David obtained 76, 65, 82, 67 and 85 marks in English, Mathematics, Physics, chemistry and biology. His average was

A. 65

B. 69

C. 72

D. 75

Ans: D

Explanation:

\text {Average} = \left ( \frac{76+65+82+67+85}{5} \right ) = \left ( \frac{375}{5} \right ) = 75

 

 

 

8. Find the average of all the numbers between 6 and 34 which are divisible by 5.

A. 18

B. 20

C. 24

D. 30

Ans: B

Explanation:

\text {Average} = \left ( \frac{10+15+20+25+30}{5} \right ) = \left ( \frac{100}{5} \right ) = 20

 

 

 

9. The average of first nine prime numbers is

\text{A. 9}

 

\text{B. 11}

 

\text{C. } 11\frac{1}{9}

 

 

\text{D. } 11\frac{22}{9}

 

 

Ans: C

Explanation:

\text{Average = } \left ( \frac{2+3+5+7+11+13+17+19+23}{9} \right ) = \frac{100}{9} = 11\frac{1}{9}

 

 

 

10. A student was asked to find arithmetic mean of the numbers 3, 11, 7, 9, 15, 13, 8, 19, 17, 21, 14 and x. He found the mean to be 12. What should be the number in place of  x ?

A. 3

B. 7

C. 17

D. 31

Ans: B

Explanation:

\text {clearly,}\left ( \frac{3+11+7+9+15+13+8+19+17+21+14+x}{12} \right ) = 12

 

 

\left ( \frac{137+x}{12} \right ) = 12

 

 

137 + x = 144

 

x = 7