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Aptitude question and answer on Average



33
The average of the first five multiples of 9 is:
A.    20
B.    27
C.    28
D.    30

Answer : B.   27

Explanation:
Required average = (total sum of multiple of 9)/5
= \((9+18+27+36+45)\over5\)
= 27

34
The average age of 50 students and a teacher is 25 years. When the teacher’s age is excluded, the average age decreases by 1 year. What is the age of the teacher?  
A.    65
B.    75
C.    74
D.    64

Answer : B.   75

Explanation:
Total age of 50 students and 1 teacher = \(25\times51 \)= 1275
Total age of the students = \(24\times50\) = 1200. ( Average age reduces by 1 when teachers age is not included )
Therefore the age of the teacher is 1275 – 1200 = 75 years.

35
Ajit has a certain average for 9 innings. In the tenth innings, he scores 100 runs thereby increasing his average by 8 runs. His new average is:
A.    20
B.    21
C.    28
D.    32

Answer : C.  28

Explanation:
Let Ajit's average be x for 9 innings. So, Ajit scored 9x run in 9 innings.
In the 10th inning, he scored 100 runs then average became (x+8). And he scored \((x+8)\times10\) runs in 10 innings.
Now,
\(=>9x+100 = 10\times(x+8)\)
Or, \(9x+100 = 10x+80\)
Or, \(x = 100-80\)
Or, x = 20
New average = \((x+8) = 28\)  runs.