169+ Problems on Average With Explanation

Q:

If the average of 31, x, 42, 39, 56, 78, 83 and 91 is 58.5, then what is the value of x?

A) 26	B) 34
C) 58	D) 48

Answer & Explanation Answer: D) 48

Explanation:

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Q:

The average monthly salary of 20 employees in an organisation is Rs. 1500. If the manager's salary is added, then the average salary increases by Rs. 100. What is the manager's monthly salary ?

A) 3600	B) 3700
C) 3800	D) 3900

Answer & Explanation Answer: A) 3600

Explanation:

Manager's monthly salary Rs. (1600 * 21 - 1500 * 20) = Rs. 3600.

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Q:

Without any stoppage, a person travels a certain distance at an average speed of 42 km/h, and with stoppages he covers the same distance at an average speed of 28 km/h. How many minutes per hour does he stop?

A) 15 minutes	B) 20 minutes
C) 18 minutes	D) 22 minutes

Answer & Explanation Answer: B) 20 minutes

Explanation:

Let the total distance to be covered is 84 kms.
Time taken to cover the distance without stoppage = 84/42 hrs = 2 hrs
Time taken to cover the distance with stoppage = 84/28 = 3 hrs.
Thus, he takes 60 minutes to cover the same distance with stoppage.
Therefore, in 1 hour he stops for 20 minutes.

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Q:

The average age of students of a class is 15.8 years. The average age of boys in the class is 16.4 years and that of the girls is 15.4 years, The ratio of the number of boys to the number of girls in the class is :

A) 1 : 2	B) 2 : 3
C) 3 : 4	D) 4 : 5

Answer & Explanation Answer: B) 2 : 3

Explanation:

Let the ratio be k : 1. Then,

k * 16.4 + 1 * 15.4 = (k + 1) * 15.8

<=> (16.4 - 15.8) k = (15.8 - 15.4) <=> k = 0.4/0.6 = 2/3.

Required ratio = 2/3 : 1 = 2 : 3.

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Q:

If the arithmetic mean of seventy-five numbers is calculated, it is 35. if each number is increased by 5, then mean of new numbers is :

A) 30	B) 40
C) 50	D) 60

Answer & Explanation Answer: B) 40

Explanation:

Let the numbers are $x_{1,} x_{2,} . . . . . . . x_{75}$

By Hypothesis , $\frac{x_{1} + x_{2} + . . . . x_{75}}{75} = 35$ ......(i)

Mean of new numbers = $\frac{(x_{1} + 5) + (x_{2} + 5) + . . . . . . . (x_{75} + 5)}{75}$

$\frac{x_{1} + x_{2} + . . . . . . x_{75} + 5 * 75}{75}$

$\frac{x_{1} + x_{2} + . . . . . . x_{75}}{75} + \frac{375}{75} = 35 + 5 = 40$ By (i)

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Q:

The average age of husband, wife and their child 3 years ago was 27 years and that of wife and the child 5 years ago was 20 years. The present age of the husband is

A) 30	B) 40
C) 50	D) 60

Answer & Explanation Answer: B) 40

Explanation:

Sum of the present ages of husband, wife and child = (27 x 3 + 3 x 3) years = 90 years.

Sum of the present ages of wife and child (20 x 2 + 5 x 2) years = 50 years.

Husband's present age = (90 - 50) years = 40 years.

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Q:

A motorist travels to a place 150 km away at an average speed of 50 km/hr and returns at 30 km/hr. His average speed for the whole journey in km/hr is :

A) 35	B) 36
C) 37.5	D) 38.2

Answer & Explanation Answer: C) 37.5

Explanation:

Average speed = (2xy) /(x + y) km/hr

= (2 * 50 * 30) / (50 + 30) km/hr.

37.5 km/hr.

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Q:

The average price of three items of furniture is Rs. 15000. If their prices are in the ratio 3:5:7, the price of the cheapest item is :

A) 6000	B) 7000
C) 8888	D) 9000

Answer & Explanation Answer: D) 9000

Explanation:

Let their prices be 3x, 5x and 7x.

Then, 3x + 5x + 7x = (15000 * 3) or x = 3000.

Cost of cheapest item = 3x = Rs. 9000.

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