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:

A family consists of grandparents, parents and three grandchildren. The average age of the grandparents is 67 years, that of the parents is 35 years and that of the grandchildren is 6 years. What is the average age of the family ?

A) 31( 5/7) B) 32 (6/7)
C) 34(4/7) D) 35(4/9)
 
Answer & Explanation Answer: A) 31( 5/7)

Explanation:

Required average = (67 * 2 + 35 * 2 + 6 * 3) / (2 + 2 + 3)

                           = (134 + 70 + 18) / 7  =  222 / 7 = 31(5/7) years.

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Q:

In an examination, a pupil's average marks were 63 per paper. If he had obtained 20 more marks for his Geography paper and 2 more marks for his History paper, his average per paper would have been 65. How many papers were there in the examination ?

A) 8 B) 9
C) 10 D) 11
 
Answer & Explanation Answer: D) 11

Explanation:

Let the number of papers be x. Then, 63x + 20 + 2 = 65x or 2x = 22 or x = 11.

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Q:

A student was asked to find the 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) 6 B) 7
C) 8 D) 9
 
Answer & Explanation Answer: B) 7

Explanation:

Clearly, we have (3 + 11 + 7 + 9 + 15 + 13 + 8 + 19 + 17 + 21 + 14 + x) / 12 = 12.

or  137 + x = 144 or x = 144 - 137 = 7.

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Q:

The average of six numbers is 3.95. The average of two of them is 3.4, while the average of the other two is 3.85. What is the average of the remaining two numbers ?

A) 3.6 B) 4.6
C) 6.5 D) 7.3
 
Answer & Explanation Answer: B) 4.6

Explanation:

 Sum of the remaining two numbers = (3.95 * 6) - [(3.4 * 2) + (3.85 * 2)]

                                                   = 23.70 - (6.8 + 7.7) = 23.70 - 14.5 = 9.20.

Required average = (9.2 / 2) =  4.6.

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Q:

The average price of 10 books is Rs. 12 while the average price of 8 of these books is Rs. 11.75. Of the remaining two books, if the price of one book is 60% more than the price of the other, what ia the pice of each of these two books ?

A) 16,12 B) 10,16
C) 23,9 D) 8,7
 
Answer & Explanation Answer: B) 10,16

Explanation:

Total pice of the two books = Rs. [(12 x 10) - (11.75 x 8)]

 

                                          = Rs. (120 - 94) = Rs. 26.

 

let the price of one book be Rs. x

 

Then, the price of other book = Rs. (x + 60% of x) = Rs.(x+(3/5)x) = Rs. (8/5)x

 

So,  x+(8/5)x =26 <=> x =10

 

The prices of the two books are Rs. 10 and Rs. 16

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Q:

The captain of a cricket team of 11 members is 26 years old and the wicket keeper is 3 years older. If the ages of these two are excluded, the average age of the remaining players is one year less than the average age of the whole team. What is the average age of the team ?

A) 20 years B) 21 years
C) 23 years D) 25 years
 
Answer & Explanation Answer: C) 23 years

Explanation:

Let the average age of the whole team be x years.

11x - (26 + 29) = 9 (x - 1)

=> 11x - 9x = 46

=> 2x = 46

=> x = 23.

So, average age of the team is 23 years.

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Q:

The average temperature of the town in the first four days of a month was 58 degrees. The average for the second, third, fourth and fifth days was 60 degrees. If the temperatures of the first and fifth days were in the ratio 7 : 8, then what is the temperature on the fifth day ?

A) 62 degrees B) 64 degrees
C) 65 degrees D) 66 degrees
 
Answer & Explanation Answer: B) 64 degrees

Explanation:

Sum of temperatures on 1st, 2nd, 3rd and 4th days = (58 * 4) = 232 degrees ... (1)

Sum of temperatures on 2nd, 3rd, 4th and 5th days - (60 * 4) = 240 degrees  ....(2)

Subtracting (1) From (2), we get :

Temp, on 5th day  - Temp on 1st day  = 8 degrees.

Let the temperatures on 1st and 5th days be 7x and 8x degrees respectively.

Then, 8x - 7x = 8 or x = 8.

Temperature on the 5th day = 8x = 64 degrees.

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Q:

Find the average of first 20 multiples of 9.

 

A) 94.8 B) 94.7
C) 94.6 D) 94.5
 
Answer & Explanation Answer: D) 94.5

Explanation:
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