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:

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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Q:

In Arun's opinion, his weight is greater than 65 kg but leas than 72 kg. His brother does not agree with Arun and he thinks that Arun's weight is greater than 60 kg but less than 70 kg. His mother's view is that his weight cannot be greater than 68 kg. If all of them are correct in their estimation, what is the average of diferent probable weights of Arun ?

A) 55.5 kg B) 66.5 kg
C) 77.5 kg D) 88.5 kg
 
Answer & Explanation Answer: B) 66.5 kg

Explanation:

Let Arun's weight be X kg.

According to Arun, 65 < X < 72.

According to Arun's brother, 60 < X < 70.

According to Arun's mother, X < 68.

The values satisfying all the above conditions are 66 and 67.

Required average = (66 + 67) / 2 = 66.5 kg

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Q:

David obtained 76, 65, 82, 67 and 85 marks (out of 100) in English, Mathematics,Physics, Chemistry and Biology What are his average marks ?

A) 75 B) 68
C) 65 D) 60
 
Answer & Explanation Answer: A) 75

Explanation:

Average =   (76 + 65 + 82 + 67 + 85 )/ 5 = 375/5   =  75.

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Q:

The mean temperature of Monday to Wednesday was 37C and of Tuesday to Thursday was 34C . If the temperature on Thursday was (4/5) th that of Monday, the temperature on Thursday was?

Answer

\inline \fn_jvn M+T+W =(37\times 3)^{0}=111^{0}C   -----------(1)


\inline \fn_jvn T+W+Th=(34\times 3)^{0}=102^{0}C


\inline \fn_jvn \Rightarrow T+W+\frac{4}{5}M = 102^{0}C                --------------(2)


(1) - (2) gives


\inline \fn_jvn \frac{1}{5} th of temperature on Monday = 


\inline \fn_jvn \Rightarrow Temperature on Monday = \inline \fn_jvn 45^{0}C


\inline \fn_jvn \therefore Temperature on Thursday = \inline \fn_jvn \frac{4}{5}\times 45^{0}=36^{0}

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Q:

The average monthly salary of 20 employees in an organisation is Rs. 1500. If the manager's salary is added, then the average salary increases by Rs. 100. What is the manager's monthly salary ?

A) 3600 B) 3700
C) 3800 D) 3900
 
Answer & Explanation Answer: A) 3600

Explanation:

Manager's monthly salary Rs. (1600 * 21 - 1500 * 20) = Rs. 3600.

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Q:

Without any stoppage, a person travels a certain distance at an average speed of 42 km/h, and with stoppages he covers the same distance at an average speed of 28 km/h. How many minutes per hour does he stop?

A) 15 minutes B) 20 minutes
C) 18 minutes D) 22 minutes
 
Answer & Explanation Answer: B) 20 minutes

Explanation:

Let the total distance to be covered is 84 kms.
Time taken to cover the distance without stoppage = 84/42 hrs = 2 hrs
Time taken to cover the distance with stoppage = 84/28 = 3 hrs.
Thus, he takes 60 minutes to cover the same distance with stoppage.
Therefore, in 1 hour he stops for 20 minutes.

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Q:

The average age of students of a class is 15.8 years. The average age of boys in the class is 16.4 years and that of the girls is 15.4 years, The ratio of the number of boys to the number of girls in the class is :

A) 1 : 2 B) 2 : 3
C) 3 : 4 D) 4 : 5
 
Answer & Explanation Answer: B) 2 : 3

Explanation:

 Let the ratio be k : 1. Then,

k * 16.4 + 1 * 15.4 = (k + 1) * 15.8

<=> (16.4 - 15.8) k = (15.8 - 15.4)  <=> k =  0.4/0.6 = 2/3.

Required ratio  = 2/3 : 1 = 2 : 3.

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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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