Practice Questions
Concept Explanation
Age problems use the same average formulas. Remember: after t years, every person's age increases by t, so the average also increases by t.
Key Rules
- Average age = Total of ages / Number of persons
- After t years, new average = Old average + t
- When a person joins or leaves, apply addition/removal formulas.
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Q1 Easy
Average age of A, B and C is 20 years. If their ages are 18, 22 and x, find x.
ExplanationTotal = 60. x = 60 − 40 = 20. -
Q2 Medium
Average age of 5 friends is 30 years. One aged 25 years leaves and one aged 35 years joins. New average is:
ExplanationNet change in sum = +10 over 5 persons → average increases by 2 → 32. -
Q3 Easy
Father is 40 and son is 10. Average of their ages is:
Explanation(40 + 10)/2 = 25 years. -
Q4 Easy
Father 40 and son 10. After 10 years, their average age will be:
ExplanationAfter 10 years: 50 and 20. Average = 35. -
Q5 Medium
Average age of 10 students is 15 years. A teacher aged 45 years joins. New average is:
Explanation(150 + 45)/11 = 17.73 years (approx). -
Q6 Easy
Average age of a family of 4 is 25 years. A new baby is born. New average age is:
ExplanationTotal = 100. With baby (age 0): 100/5 = 20 years. -
Q7 Easy
Two years ago, average age of 5 friends was 20 years. Present average age is:
ExplanationEach person is 2 years older → average increases by 2 → 22.
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Q8 Medium
Average age of 6 persons is 24 years. A person aged 38 years joins. New average is:
Explanation(144 + 38)/7 = 182/7 = 26 years. -
Q9 Easy
Average age of 4 members is 28 years. After 5 years, average age will be:
ExplanationEach member gains 5 years → average increases by 5 → 33 years. -
Q10 Easy
The average age of father and son is 30 years. If the father is 44 years old, the son's age is:
ExplanationTotal = 60. Son = 60 − 44 = 16 years. -
Q11 Medium
Average age of 8 persons is 25 years. One person aged 32 years leaves. New average is:
Explanation(200 − 32)/7 = 168/7 = 24 years. -
Q12 Easy
Present average age of 4 members is 28 years. After 5 years, average age will be:
ExplanationEach member gains 5 years → average increases by 5 → 33 years. -
Q13 Medium
Average age of 5 members is 40 years. A person aged 50 years joins. New average is:
Explanation(200 + 50)/6 = 250/6 = 41.67 years (approx). -
Q14 Easy
The sum of ages of A and B is 48 years and their average is 24 years. After 6 years, their average age will be:
ExplanationAverage increases by 6 years → 24 + 6 = 30 years.
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DS1 Easy
What is the average age?
Statement IThe ages of three persons are 18, 22 and 20 years.
Statement IIThe sum of their ages is 60 years.
ExplanationEach statement alone gives average = 60/3 = 20 years. -
DS2 Medium
What is the son's age?
Statement IThe average age of father and son is 30 years.
Statement IIThe father is 44 years old.
ExplanationTogether: total = 60, son = 60 − 44 = 16 years.
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DS3 Easy
What will the average age be after 5 years?
Statement IThe present average age is 28 years.
Statement IIThere are 4 members in the group.
ExplanationStatement I alone: after 5 years average = 28 + 5 = 33 years. -
DS4 Medium
What is the new average age after a person joins?
Statement IAverage age of 6 persons is 24 years.
Statement IIThe person who joins is 38 years old.
ExplanationTogether: (144 + 38)/7 = 26 years.