Average Practice Questions

5 questions per page • Detailed step-by-step solutions

Question 21
Hard
The average weight of A, B and C is 62 kg. When D joins them, the average becomes 59.75 kg. If E, whose weight is 4 kg more than D's, replaces A, the average weight of B, C, D and E becomes 61 kg. What is the weight of A?
A 52 kg
B 53 kg
C 57 kg
D 56 kg
Correct Answer: A

Explanation:

Step 1: A + B + C = 3 × 62 = 186; A + B + C + D = 4 × 59.75 = 239, so D = 239 − 186 = 53 kg. Step 2: E = D + 4 = 57 kg; B + C + D + E = 4 × 61 = 244, so B + C = 244 − 53 − 57 = 134. Step 3: A = (A + B + C) − (B + C) = 186 − 134 = 52 kg.
Question 22
Easy
The average weight of 12 students in a class is 60 kg. When a new student joins, the average weight increases by 1 kg. What is the weight of the new student?
A 72 kg
B 73 kg
C 61 kg
D 74 kg
Correct Answer: B

Explanation:

Step 1: Old total = 12 × 60 = 720 kg. Step 2: New total = 13 × 61 = 793 kg. Step 3: New member = 793 − 720 = 73 kg.
Question 23
Medium
Three classes have 47, 27 and 31 students with average marks 52, 53 and 85 respectively. What are the average marks of all the students together?
A 63.33
B 63
C 61
D 62
Correct Answer: D

Explanation:

Step 1: Class totals: 47 × 52 = 2444, 27 × 53 = 1431, 31 × 85 = 2635. Step 2: Grand total = 6510; total students = 47 + 27 + 31 = 105. Step 3: Overall average = 6510 ÷ 105 = 62.
Question 24
Medium
The average of 17 results is 50. The average of the first 9 results is 44 and the average of the last 9 results is 58. Find the 9th result.
A 118
B 68
C 51
D 77
Correct Answer: B

Explanation:

Step 1: Sum of all 17 results = 17 × 50 = 850. Step 2: Sum of the first 9 = 9 × 44 = 396; sum of the last 9 = 9 × 58 = 522. Together they cover 18 results, i.e. all 17 plus the 9th result once more. Step 3: 9th result = 396 + 522 − 850 = 68.
Question 25
Medium
When a couple married, their average age was 26 years. After 9 years, with a child born in between, the average age of the family of three is 26 years. What is the present age of the child?
A 9 years
B 10 years
C 8 years
D 1 year
Correct Answer: C

Explanation:

Step 1: At marriage the couple's total age = 2 × 26 = 52 years. Step 2: After 9 years each is 9 years older: 52 + 2 × 9 = 70 years. Step 3: Family total now = 3 × 26 = 78, so child's age = 78 − 70 = 8 years.