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:

In an NGO the daily average wages of 20 illiterate employees is decreased from Rs.25 to Rs.10, thus the average salary of  all the literate and illiterate  employees is decreased Rs.10 per day. The No. of educated employees working in the NGO is :

A) 15 B) 20
C) 10 D) Data Insufficient
 
Answer & Explanation Answer: C) 10

Explanation:

Total employees = 25-10×2010=30

 Hence number of educated employees  = 30-20 = 10

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Q:

The average weight of a group of boys is 30 kg. After a boy of weight 35 kg joins the group, the average weight of the group goes up by 1 kg. Find the number of boys in the group originally ?

A) 6 B) 8
C) 4 D) 5
 
Answer & Explanation Answer: C) 4

Explanation:

Let the number of boys in the group originally be x.
Total weight of the boys = 30x
After the boy weighing 35 kg joins the group, total weight of boys = 30x + 35
So 30x + 35 + 31(x + 1) = > x = 4.

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Q:

The average age of a group of persons going for picnic is 16 years. Twenty new persons with an average age of 15 years join the group on the spot due to which their average age becomes 15.5 years. The number of persons initially going for picnic is :

A) 15 B) 20
C) 23 D) 24
 
Answer & Explanation Answer: B) 20

Explanation:

Let the initial number of persons be x. Then,

16x + 20 * 15 = 15.5 (x + 20) <=> 0.5x = 10 <=> x = 20.

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Q:

The average of any 5 consecutive odd natural numbers is k . If two more such numbers , just next to the previous 5 numbers are added , the new average becomes

A) 2(k+1) B) 2k-3
C) 2k+1 D) k+2
 
Answer & Explanation Answer: D) k+2

Explanation:

The 5 consecutive odd numbers whose average is k are  (k-4), (k-2), k, (k+2), (k+4)

Again the average of (k-4), (k-2), k, (k+2), (k+4), (k+6), (k+8) is (k+2)

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Q:

16 children are to be divided into two groups A and B of 10 and 6 children. The average percent marks obtained by the children of group A is 75 and the average percent marks of all the 16 children is 76. What is the average percent marks of children of group B ?

A) 233/3 B) 243/4
C) 254/5 D) 345/7
 
Answer & Explanation Answer: A) 233/3

Explanation:

 Required average = [(76 * 16) - (75 * 10)] / 6 = (1216 - 750)/6 = 466/3 = 233 /3.

 

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Q:

What will be the cost of building a fence around a square plot with area equal to 289 sq ft, if the price per foot of building the fence is Rs. 58 ?

A) Rs. 3748 B) Rs. 3847
C) Rs. 3944 D) Rs. 3154
 
Answer & Explanation Answer: C) Rs. 3944

Explanation:

Let the side of the square plot be 'a' ft.
Given area of the plot (a x a) = 289 => a = 17
Length of the fence = Perimeter of the plot = 4a = 68 ft.
Cost of building the fence = 68 x 58 = Rs. 3944.

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Q:

The average age of the boys in a class is 16 years and that of the girls is 15 years. The average age for the whole class is :

A) 15 B) 20
C) 21 D) data inadequate
 
Answer & Explanation Answer: D) data inadequate

Explanation:

 Clearly, to find the average, we ought to know the number of boys, girls or students in the class, neither of which has been given.

So, the data provided is inadequate.

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Q:

What is the average of four tenths and five thousandths

A) 25002 B) 2502
C) 0.2025 D) none
 
Answer & Explanation Answer: C) 0.2025

Explanation:

Four tenths = 0.4

Five thousandths = 0.005

The average is (0.4 + 0.005)/2 = 0.2025

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