169+ Problems on Average With Explanation

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:

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:

In a class of 78 students 41 are taking French, 22 are taking German. Of the students taking French or German, 9 are taking both courses. How many students are not enrolled in either course?

A) 6	B) 12
C) 24	D) 18

Answer & Explanation Answer: C) 24

Explanation:

You could solve this by drawing a Venn diagram. A simpler way is to realize that you can subtract the number of students taking both languages from the numbers taking French to find the number taking only French. Likewise find those taking only German. Then we have:Total = only French + only German + both + neither

78 = (41-9) + (22-9) + 9 + neither.

Not enrolled students = 24

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Q:

The average age of 15 students of a class is 15 years. Out of these, the average age of 5 students is 14 years and that of the other 9 students is 16 years, The age of the 15th student is :

A) 11	B) 12
C) 13	D) 14

Answer & Explanation Answer: A) 11

Explanation:

Age of the 15th student = [15 * 15 - (14 * 5 + 16 * 9)] = (225-214) = 11 years.

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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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Q:

The average value of property of Mittal, Ambani and Singhania is Rs.11111 crore. The property of Singhania is as less than the property of Mittal is greater than the average property of both the Singhania and Mittal. The value of property of Ambani is :

A) Rs.111 crore	B) Rs. 1111 crore
C) Rs. 11111 crore	D) can't be determined

Answer & Explanation Answer: C) Rs. 11111 crore

Explanation:

$\frac{M + A + S}{3} = 11111$

also $\frac{S + M}{2} = 11111$ ( $∵$ M - 11111 = 11111 - S)

=>A = 11111

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