Some questions on Averages with answers and explanations

Here are some questions on averages for who preparing for competitive exams. 

1.The average of first five multiples of 3 is:

	A.	8
	B.	9
	C.	10
	D.	11

Solution:
Option (B) is correct

Basic Formula:  1,2,3...n

If n is odd, the formula is (n+12)th term
The five multiples of 3 is 3,6,9,12,15 (n+12)⇒(5+12)th term
⇒(62)th term = 3rd term
Here 3rd  term is 9

2.There are two sections A and B of a class, consisting of 36 and 44 students’ respectively. If the average   weight of section A is 40kg and that of section B is 35kg, find the average weight of the whole class.

	A.	30.00 kg
	B.	35.00 kg
	C.	37.25 kg
	D.	42.50 kg

Solution:
Option (C) is correct

Total weight of (36+44=80)

Students =(36×40+44×35) kg = 2980 kg
Therefore average weight of the whole class =(298080)Therefore average weight = 37.25kg

3.	In the first 10 overs of a cricket game, the run rate was only 3.2. What should be the run rate in the remaining 40 overs to reach the target of 282 runs?
	A. 6.25 B. 6.5 C. 6.75 D. 7

Solution:
Option (A) is correct

Required run rate =		282 - (3.2 x 10)/40		=	250/40	= 6.25

4.A Batsman makes a score of 87 runs in the 17th inning and thus increases his average by 3. Find his average after 17th inning.

	A.	40
	B.	39
	C.	52
	D.	55

Solution:
Option (B) is correct

Let the average after 17th innings = x

Then average after 16th innings = (x−3)
 
Therefore 16(x−3)+87=17x
 
Therefore x=39

5.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.	65
	B.	69
	C.	75
	D.	None of above

Solution:
Option (C) is correct

Average
=76+65+82+67+855

=3755
=75