100+ Average Questions for Competitive Exams with Solutions - 1

Question: 1

Mean of eight numbers is 38.4 and the mean of seven of them is 39.2. What is the eight number?

(A) 3.2

(B) 31.2

(C) 32.8

(D) 34.8

Ans: C

Sum of eight numbers = 8 × 38.4 = 307.2

Sum of seven numbers = 7 x 39.2 = 274.4

∴ Eighth number = 307.2 – 274.4 = 32.8.

Question: 2

In seven given numbers, the average of first four numbers is 4 and that of the last four numbers is also 4. If the average of these seven numbers is 3, the fourth number is

(A) 4

(B) 7

(C) 11

(D) 13

Ans: C

Fourth number = ( 4 × 4 + 4 × 4 – 7 × 3) = 11.

Question: 3

Find the average of all the numbers between 6 and 34 which are divisible by 5.

(A) 18

(B) 19

(C) 20

(D) 22

Ans: C

Average = $$({10 + 15 + 20 + 25 + 30} / {2})$$ = $${100} / {5}$$ = 20.

Question: 4

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 years

(B) 15.5 years

(C) 16 years

(D) Cannot be computed with the given information

Ans: D

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.

Question: 5

The average of five numbers is 306.4. The average of the first two numbers is 431 and the average of the last two numbers is 2145. What is the third number?

(A) 108

(B) 241

(C) 321

(D) 411

Ans: B

Third number = [306.4 × 5 – (431 × 2 + 324.5 × 2)]

= (1532 - 1291) = 241.

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