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 of five numbers is 27. If one number is excluded, the average becomes 25. The excluded number is :

A) 25 B) 35
C) 45 D) 55
 
Answer & Explanation Answer: B) 35

Explanation:

Excluded number = (27 x 5)  -  (25 x 4) = 135 - 100 = 35.

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Q:

How many window coverings are necessary to span 50 windows, if each window covering is 15 windows long?

A) 4 B) 15
C) 3 D) 50
 
Answer & Explanation Answer: A) 4

Explanation:

Given that, 

Number of windows = 50

Each window covering covers 15 windows

=> 50 windows requires 50/15 window coverings

= 50/15 = 3.333

 

Hence, more than 3 window coverings are required. In the options 4 is more than 3. 

 

Hence, 4 window coverings are required to cover 50 windows of each covering covers 15 windows.

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Q:

If the average of 31, x, 42, 39, 56, 78, 83 and 91 is 58.5, then what is the value of x?

 

A) 26 B) 34
C) 58 D) 48
 
Answer & Explanation Answer: D) 48

Explanation:
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Q:

The average of two numbers is 10 and the product of two numbers is 96. Find the two numbers.

 

 

A) 3, 32 B) 12, 8  
C) 1, 96   D) 24, 4
 
Answer & Explanation Answer: B) 12, 8  

Explanation:
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Q:

Find the range of the data 9, 5, 9, 3, 4, 7, 8, 4, 8, 9, 5, 9.

 

A) 3 B) 5
C) 6 D) 4
 
Answer & Explanation Answer: C) 6

Explanation:
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Q:

Consider the following frequency distribution:

x     f

8     6

5     4

6     5

10    8

9     9

4     6

7     4

What is the median for the distribution?

A) 6 B) 7
C) 8 D) 9
 
Answer & Explanation Answer: C) 8

Explanation:
Summation of frequencies = 6+4+5+8+9+6+4 = 42
Median = mid value = average of 21st and 22nd value
Arranging data in increasing order we get

x     f

4     6

5     4

6     5

7     4

8     6

9     9

10    8

 
So mid value i.e 21st and 22nd value = 8
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Q:

In a village the average age of n people is 42 years. But after the verification it was found that the age of a person had been  considered 20 years less than the actual age, so the new average, after the correction,increased by 1. The value of n is :

A) 21 B) 20
C) 22 D) None of these
 
Answer & Explanation Answer: B) 20

Explanation:

It is the same as a person with 20 years more age  replaces an existing person of the group ( or village)

Since the total age of the village having n persons, is being increased by 20 years and the average age of village is being increased by 1 year, hence there are total 20 people in the village.

 

Alternatively :  ( n x 42 ) + 20 = ( n x 43 )

                          => n=20

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Q:

The ratio of speeds of a car, a train and a bus is 5:9:4. The average speed of the car, the bus and the train is 72 km/hr together. What is the average speed of the car and the train together ?

A) 84 km/hr B) 96 km/hr
C) 72 km/hr D) 60 km/hr
 
Answer & Explanation Answer: A) 84 km/hr

Explanation:

Let the speeds of the car, train and bus be 5x, 9x and 4x km/hr respectively.
Average speed = 5x + 9x + 4x/3 = 18x /3 = 6x km/hr.
Also, 6x = 72 => x = 12 km/hr
Therefore, the average speed of the car and train together is = 5x+9x2= 7x = 7 x 12 = 84 km/hr.

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