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Aptitude miscellaneous
  1. The average age of 30 students is 9 years. If the age of their teacher is included, the average age becomes 10 years. The age of the teacher (in years) is








  1. View Hint View Answer Discuss in Forum

    Given , The average age of 30 students = 9 years.
    Total age of 30 students = 9 × 30 = 270 years
    The average age of 30 students and a teacher = 10 years.
    Total age of 30 students and a teacher = 31 × 10 = 310 years
    Age of the teacher = Total age of 30 students and a teacher – Total age of 30 students

    Correct Option: D

    Given , The average age of 30 students = 9 years.
    Total age of 30 students = 9 × 30 = 270 years
    The average age of 30 students and a teacher = 10 years.
    Total age of 30 students and a teacher = 31 × 10 = 310 years
    Age of the teacher = Total age of 30 students and a teacher – Total age of 30 students
    ∴ Age of the teacher = 310 – 270 = 40 years

  1. There were 24 students in a class. One of them, who was 18 years old, left the class and his place was filled up by a newcomer. If the average of the class thereby, was lowered by one month, the age of the newcomer is








  1. View Hint View Answer Discuss in Forum

    Here , Age of replaced student = 18 years
    Total age decrease = 24 × 1 = 24 months = 2 years
    ∴ Age of newcomer = Age of replaced student - Total age decrease

    Correct Option: C

    Here , Age of replaced student = 18 years
    Total age decrease = 24 × 1 = 24 months = 2 years
    ∴ Age of newcomer = Age of replaced student - Total age decrease
    Hence , Age of newcomer = 18 – 2 = 16 years.

  1. The average age of 24 boys and their teacher is 15 years. When the teacher’s age is excluded, the average age decreases by 1 year. The age of the teacher is








  1. View Hint View Answer Discuss in Forum

    Given that , The average age of 24 boys and their teacher = 15 years.
    Total age of 24 boys and teacher = (24 + 1) × 15
    When the teacher’s age is excluded, Total decrease age = 24 × (15 – 1)
    The age of the teacher = (24 + 1) × 15 – 24 × (15 – 1)

    Correct Option: B

    Given that , The average age of 24 boys and their teacher = 15 years.
    Total age of 24 boys and teacher = (24 + 1) × 15
    When the teacher’s age is excluded, Total decrease age = 24 × (15 – 1)
    The age of the teacher = (24 + 1) × 15 – 24 × (15 – 1)
    ∴ The age of the teacher = 25 × 15 – 24 × 14 = 375 – 336 = 39 years.

  1. The average age of 30 boys in a class is 15 years. One boy aged 20 years, left the class, but two new boys came in his place whose ages differ by 5 years. If the average age of all the boys now in the class still remains 15 years, the age of the younger newcomer is :








  1. View Hint View Answer Discuss in Forum

    Let the age of younger boy be y years.
    ∴ Age of older boy = (y + 5) years.
    The average age of 30 boys in a class = 15 years
    Then, total age of 30 boys = 30 × 15 = 450 years.
    Total age of 31 boys after two newcomers join & 1 left = 450 – 20 + y + y + 5 = 435 + 2y
    Clearly, 435 + 2y = 31 × 15

    Correct Option: B

    Let the age of younger boy be y years.
    ∴ Age of older boy = (y + 5) years.
    The average age of 30 boys in a class = 15 years
    Then, total age of 30 boys = 30 × 15 = 450 years.
    Total age of 31 boys after two newcomers join & 1 left = 450 – 20 + y + y + 5 = 435 + 2y
    Clearly, 435 + 2y = 31 × 15
    ⇒ 2y = 465 – 435
    ⇒ y = 30 ÷ 2 = 15 years

  1. When the average age of a husband and wife and their son was 42 years, the son got married and a child was born just one year after the marriage. When child turned to be five years then the average age of family became 36 years. What was the age of daughter-in-law at the time of marriage?








  1. View Hint View Answer Discuss in Forum

    Given that , Average of ( Husband + Wife + Son ) = 42 years
    Total age of ( Husband + Wife + Son ) = 42 × 3 = 126 years
    Total age of (Husband + Wife + Son) + Daughter + Child = 36 × 5 = 180
    ⇒ (126 + 6 × 3) + Daughter + Child = 180
    ⇒ (126 + 18) + Daughter + Child = 180
    ⇒ 144 + Daughter + Child = 180
    ⇒ Daughter + Child = 180 – 144 = 36

    Correct Option: C

    Given that , Average of ( Husband + Wife + Son ) = 42 years
    Total age of ( Husband + Wife + Son ) = 42 × 3 = 126 years
    Total age of (Husband + Wife + Son) + Daughter + Child = 36 × 5 = 180
    ⇒ (126 + 6 × 3) + Daughter + Child = 180
    ⇒ (126 + 18) + Daughter + Child = 180
    ⇒ 144 + Daughter + Child = 180
    ⇒ Daughter + Child = 180 – 144 = 36
    ∴ Age of daughter-in-law at the time of marriage (D) = 36 – (6 + 6) = 24 years