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 car owner buys petrol at Rs 7.50, Rs. 8 and Rs. 8.50 per litre for three successive years. What approximately is the average cost per litre of petrol if he spends Rs. 4000 each year ?

A) 6.23 B) 7.98
C) 8.97 D) 9.89
 
Answer & Explanation Answer: B) 7.98

Explanation:

Total quantity of petrol consumed in 3 years =(4000/7.50+4000/8+4000/8.50)  liters

 

                                                         = 4000(2/15+1/8+2/17) liters                                                   

 

                                                         = 76700/51 liters

 

Total amount spent = Rs. (3 x 4000) = Rs. 12000.

 

Average cost = Rs. (12000*51/76700) = Rs. 7.98.

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57 38881
Q:

The average age of a husband and his wife was 23 years at the time of their marriage. After  five years they have a one-year old child. The average age of the family now is : 

A) 25 B) 23
C) 19 D) 18
 
Answer & Explanation Answer: C) 19

Explanation:

Sum of the present ages of husband, wife and child = (23 * 2 + 5 * 2) + 1 = 57 years.

Required average = (57/3) = 19 years.

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78 37455
Q:

Of the four numbers, whose average is 60, the first is one-fourth of the sum of the last three. The first number is :

A) 17 B) 29
C) 36 D) 48
 
Answer & Explanation Answer: D) 48

Explanation:

Let the first number be x,

Then, sum of the four numbers = x + 4x = 5x.

so,  5x/4 = 60 or x = (60 * 4) / 5 = 48.

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Q:

The average salary of all the workers in a workshop is Rs. 8000. The average salary of 7 technicians is Rs. 12000 and the average salary of the rest is Rs. 6000. The total number of workers in the workshop is :

A) 20 B) 21
C) 23 D) 24
 
Answer & Explanation Answer: B) 21

Explanation:

 Lot the total number of workers be v Then,

8OOOv = (12000 * 7) + 6000 (v - 7) <=>  2000v = 42000  <=>  v = 21.

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64 34672
Q:

A team of 8 persons joins in a shooting competition. The best marksman scored 85 points. If he had scored 92 points, the average score for the team would have been 84. The number of points, the team scored was :

A) 665 B) 657
C) 658 D) 678
 
Answer & Explanation Answer: A) 665

Explanation:

Let the total score be x.

(x + 92 - 85) / 8 = 84.

So,  x + 7 = 672   => x = 665.

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59 33541
Q:

A certain factory employed 600 men and 400 women and the average wager was Rs. 25.50 per day, If a woman got Rs. 5 less than a man, then what are their daily wages ?

A) m:25.50 w:27.50 B) m:27.50 w:22.50
C) m:26.50 w:27.50 D) m: 24.50 w:26.50
 
Answer & Explanation Answer: B) m:27.50 w:22.50

Explanation:

Let the daily wage of a man be Rs. x.

Then, daily wage of a woman = Rs. (x - 5).

Now, 600x + 400 (x - 5) = 25.50 * (600 + 400) <=>  1000x = 27500 <=>  x = 27.50.

Man's daily wages = Rs. 27.50; Woman's daily wages = (x - 5) = Rs. 22.50.

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54 32996
Q:

Out of 9 persons, 8 persons spent Rs. 30 each for their meals. The ninth one spent Rs. 20 more than the average expenditure of all the nine. The total money spent by all of them was : 

A) Rs. 292.50 B) Rs. 297.50
C) Rs. 298 D) Rs. 298.50
 
Answer & Explanation Answer: A) Rs. 292.50

Explanation:

Let the average expenditure be Rs. x Then,

 

9x=[(8*30)+(x+20)]<=>9x =x+260 <=> x =32.50

 

Total money spent = 9x =  Rs. (9 x 32.5O) = Rs 292. 50

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95 32435
Q:

A batsman in his 17th innings makes a score of 85 and their by increasing his average by 3. What is his average after the 17th innings ?

A) 34 B) 36
C) 35 D) 37
 
Answer & Explanation Answer: D) 37

Explanation:

16x + 85 = 17(x + 3)

x = 34 + 3 = 37

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