Average


  1. Three year ago, the average age of a family of five members was 27 yr. The present average age is also 27 yr after the inclusion of a child into the family. Find the age of the child.









  1. View Hint View Answer Discuss in Forum

    Total age of 5 memeber (3 yr ago) = 27 x 5 = 135 yr
    Total age of 5 members (at present) = 135 + 5 x 3 = 150 yr.
    Let the persent age of child = x
    ∴ 27 = (150 + x)/6

    Correct Option: B

    Total age of 5 memeber (3 yr ago) = 27 x 5 = 135 yr
    Total age of 5 members (at present) = 135 + 5 x 3 = 150 yr.
    Let the persent age of child = x
    ∴ 27 = (150 + x)/6
    ⇒ x = 162 - 150 = 12 yr.


  1. The average age of three boys is 15 yr. If the ratio of their ages is 3 : 5 : 7, What is the age of the oldest boy ?











  1. View Hint View Answer Discuss in Forum

    Total age of all three boys
    = 3 x 15 = 45 yr
    Ratio of ages = 3 : 5 : 7

    Correct Option: D

    Total age of all three boys
    = 3 x 15 = 45 yr
    Ratio of ages = 3 : 5 : 7
    ∴ Age of the oldest boy
    = [7/(3 + 5 + 7)] x 45 = (7/15) x 45 = 21 yr



  1. Nine friends have dinner in a hostel. Eight of them spent ₹ 12 each on their meals and the ninth spent ₹ 16 more than the average expenditure of all the nine. Find out the total money spent by them ?











  1. View Hint View Answer Discuss in Forum

    Let average expenditure of 9 persons = x.
    According to the question,
    12 x 8 + (x + 16) = 9x

    ∴ Total money spent = 9x

    Correct Option: A

    Let average expenditure of 9 persons = x.
    According to the question,
    12 x 8 + (x + 16) = 9x
    ⇒ 8x = 112
    ⇒ x = 112/8 = 14
    ∴ Total money spent = 9x = 9 x 14 = ₹ 126


  1. In a certain examination, the average marks of an examinee is 64 per paper. if he had obtained 18 more marks for his Mathematics paper and 4 more marks for his English paper, his average per paper would have been 66. How many papers were there in the examination ?











  1. View Hint View Answer Discuss in Forum

    Let the number of papers = x.
    According to the question,
    64x + 18 + 4 = 66x

    Correct Option: A

    Let the number of papers = x.
    According to the question,
    64x + 18 + 4 = 66x
    ∴ 2x = 22
    ∴ x = 22/2 = 11



  1. The average markes obtained by 120 students in an examination is 30. if the aveage marks of passed students is 40 and that of the failed students is 10. what is the 25% of the number of students who passed the examination ?









  1. View Hint View Answer Discuss in Forum

    Let number of passed students = N
    Total marks = 120 x 30

    According to the question,
    40N + (120 - N) x 10 = 120 x 30

    Correct Option: B

    Let number of passed students = N
    Total marks = 120 x 30

    According to the question,
    40N + (120 - N) x 10 = 120 x 30
    ⇒ 3600 = 40N + 1200 - 10N
    ⇒ 30N = 2400
    ∴ N = 2400/30 = 80
    ∴ 25% of 80 = 80/4 = 20