Practice Questions
Concept Explanation
Average DS questions hinge on whether statements provide enough data for sum ÷ count or weighted totals.
Standard Answer Choices
- A — Statement I alone is sufficient; Statement II alone is not.
- B — Statement II alone is sufficient; Statement I alone is not.
- C — Both together are sufficient, neither alone.
- D — Either statement alone is sufficient.
- E — Neither alone nor together is sufficient.
Average DS Focus
Use Average = Total ÷ Count. Weighted average needs each group’s size and average.
Common Traps in Average Problems
- Averaging averages without weights.
- Forgetting to update count when a value is added.
- Confusing median with arithmetic mean.
-
Q1 Easy
Average of 20, 30, 40 is:
Explanation(20+30+40)/3 = 30. -
Q2 Easy
Average of five numbers is 18. Their sum is:
ExplanationSum = 18 × 5 = 90. -
Q3 Easy
Average of 12 numbers is 15. Sum is:
Explanation12 × 15 = 180. -
Q4 Easy
Average age of 4 persons is 25 years. Total age is:
Explanation4 × 25 = 100 years. -
Q5 Easy
Marks: 72, 78, 84, 90. Average is:
Explanation324/4 = 81. -
Q6 Medium
For “What is the average?” — I: sum = 240; II: count = 8. DS answer?
ExplanationAverage = sum/count. Need both. -
Q7 Hard
Class A: 30 students, avg 60; Class B: 20 students, avg 70. Combined average is:
ExplanationTotal marks = 3200; students = 50; avg = 64.
-
Q8 Medium
Average of first n natural numbers for n = 10 is:
Explanation(n+1)/2 = 5.5. -
Q9 Medium
When 50 is added to a set of 5 numbers with average 20, new average with 6 numbers is:
ExplanationOld sum = 100; new sum = 150; new avg = 25. -
Q10 Hard
Average weight of 10 bags is 8 kg; one bag of 14 kg is added. New average of 11 bags is:
ExplanationTotal = 80 + 14 = 94; avg = 94/11 ≈ 8.55 kg. -
Q11 Medium
For “What is the missing score?” — I: average of 4 tests is 75; II: three scores are 70, 80, 72. DS answer?
ExplanationNeed total from I and three known scores from II: missing = 300 − 222 = 78. -
Q12 Easy
Runs in 5 innings: 40, 52, 0, 68, 90. Average is:
Explanation250/5 = 50. -
Q13 Medium
Average of 8 numbers is 12. If each number is increased by 3, new average is:
ExplanationAdding 3 to each of 8 numbers adds 3 to the average. -
Q14 Hard
For “Is the average above 50?” — I: sum = 520; II: there are 10 values. DS answer?
ExplanationAverage = 520/10 = 52 > 50. Need both sum and count.
-
DS1 Easy
What is the average of a set of numbers?
Statement IThe sum of the numbers is 240.
Statement IIThere are 8 numbers in the set.
ExplanationAverage = sum/count. Need both statements. -
DS2 Medium
What is the average age of 4 persons?
Statement ITheir total age is 100 years.
Statement IIThe oldest person is 30 years old.
ExplanationStatement I: average = 100/4 = 25. Statement II alone does not fix the average.
-
DS3 Hard
What is the combined average of two classes?
Statement IClass A has 30 students with average 60.
Statement IIClass B has 20 students with average 70.
ExplanationNeed both class sizes and averages: combined = 3200/50 = 64. -
DS4 Medium
What is the missing fifth test score?
Statement IThe average of five tests is 75.
Statement IIThe first four scores are 70, 80, 72, and 78.
ExplanationTotal = 375 from I; sum of four = 300 from II; missing = 75. Neither alone suffices.