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:

 The average age of 8 men is increased by years when two of them whose ages are 21 years and 23 years are replaced by two new men. The average age of the two new men is :

A) 20 B) 30
C) 40 D) 50
 
Answer & Explanation Answer: B) 30

Explanation:

Total age increased = (8 * 2) years = 16 years.

Sum of ages of two new men = (21 + 23 + 16) years = 60 years

Average age of two new men = (60/2) years = 30 years.

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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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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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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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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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Q:

Consider the following grouped frequency distribution:

  x           f

0-10       8

10-20     12

20-30     10

30-40      p

40-50      9

 

If the mean of the above data is 25.2, then what is the value of p?

 

A) 9 B) 10
C) 11 D) 12
 
Answer & Explanation Answer: C) 11

Explanation:
Mean = (sum of fixi/ (sum of f) = (8*5 + 12*15 + 10*25 + P*35 +9*45) / (8+12+10+P+9) = 25.2
(875 + 35P)/(39+P) = 25.2
P = 11
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Q:

The average age of 36 students in a group is 14 years. When teacher's age is included to it, the average increases by one. What is the teacher's age in years ?

A) 35 years B) 45 years
C) 51 years D) 54 years
 
Answer & Explanation Answer: C) 51 years

Explanation:

Age of the teacher = (37 * 15 - 36 * 14) years = 51 years.

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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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