Average - Questions and Answers - Arithmetic Aptitude

1.

What is the average of the first five prime numbers?

A
5.0
B
5.4
C
5.6
D
6.0

View Answer

Answer: Option C

Explanation:

The first five prime numbers are 2, 3, 5, 7, and 11. Their sum is \(2 + 3 + 5 + 7 + 11 = 28\). The average is \(28 / 5 = 5.6\).

2.

The average of 5 numbers is 20. If each number is multiplied by 3, what is the new average?

A
20
B
40
C
60
D
80

View Answer

Answer: Option C

Explanation:

If every term in a set is multiplied by a constant \(n\), the average of the set is also multiplied by \(n\). Therefore, the new average is \(20 \times 3 = 60\).

3.

A student scores 70, 80, and 90 in three subjects. What must he score in the fourth subject to have an average of 85?

A
85
B
90
C
95
D
100

View Answer

Answer: Option D

Explanation:

To have an average of 85 across 4 subjects, the total score must be \(85 \times 4 = 340\). The current total is \(70 + 80 + 90 = 240\). The required score is \(340 - 240 = 100\).

4.

What is the average of the first 50 natural numbers?

A
25.0
B
25.5
C
26.0
D
26.5

View Answer

Answer: Option B

Explanation:

The average of the first \(n\) natural numbers is given by the formula \(\frac{n+1}{2}\). For \(n=50\), the average is \(\frac{50+1}{2} = 25.5\).

5.

The average age of a class of 10 students is 12 years. If the teacher's age is included, the average increases by 1. Find the teacher's age.

A
22 years
B
23 years
C
24 years
D
25 years

View Answer

Answer: Option B

Explanation:

Total age of 10 students = \(10 \times 12 = 120\). Total age of 11 people (including teacher) = \(11 \times 13 = 143\). Teacher's age = \(143 - 120 = 23\) years.

6.

The average weight of 8 persons increases by 2.5 kg when a person weighing 65 kg is replaced by a new person. Find the weight of the new person.

A
75 kg
B
80 kg
C
85 kg
D
90 kg

View Answer

Answer: Option C

Explanation:

The total increase in weight is \(8 \times 2.5 = 20\) kg. Since the new person replaced someone weighing 65 kg and caused this increase, the new person's weight is \(65 + 20 = 85\) kg.

7.

The average of 11 results is 50. The average of the first six is 49 and that of the last six is 52. Find the sixth result.

A
52
B
54
C
56
D
58

View Answer

Answer: Option C

Explanation:

Sum of all 11 results = \(11 \times 50 = 550\). Sum of first six = \(6 \times 49 = 294\). Sum of last six = \(6 \times 52 = 312\). The sixth result is counted in both groups, so \((294 + 312) - 550 = 606 - 550 = 56\).

8.

The average age of a family of 4 members was 18 years, 3 years ago. A baby being born, the average age of the family is the same today. Find the baby's age.

A
4 years
B
5 years
C
6 years
D
7 years

View Answer

Answer: Option C

Explanation:

Total age 3 years ago = \(4 \times 18 = 72\). Current total age of those 4 members = \(72 + (4 \times 3) = 84\). Current total age of 5 members (including baby) = \(5 \times 18 = 90\). Baby's age = \(90 - 84 = 6\) years.

9.

The average of 7 consecutive numbers is 20. Find the largest of these numbers.

A
21
B
22
C
23
D
24

View Answer

Answer: Option C

Explanation:

In a set of consecutive numbers, the average is the middle term. For 7 numbers, the 4th term is 20. The 5th is 21, 6th is 22, and the 7th (largest) is 23.

10.

A batsman has an average of 30 runs in 10 innings. How many runs must he score in the next inning to raise his average to 35?

A
75
B
80
C
85
D
90

View Answer

Answer: Option C

Explanation:

Total runs in 10 innings = \(10 \times 30 = 300\). Total runs needed for 11 innings to average 35 = \(11 \times 35 = 385\). Required runs = \(385 - 300 = 85\).

Exercise : Average - General Questions