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Aptitude miscellaneous
  1. The average of 20 numbers is 12. The average of the first 12 numbers is 11 and that of the next 7 numbers is 10. The last number is :








  1. View Hint View Answer Discuss in Forum

    Here , Sum of 20 numbers = 20 × 12
    sum of first 12 numbers = 11 × 12
    sum of next 7 numbers = 7 × 10
    ∴ Last number = Sum of 20 numbers – sum of first 12 numbers – sum of next 7 numbers

    Correct Option: B

    Here , Sum of 20 numbers = 20 × 12
    sum of first 12 numbers = 11 × 12
    sum of next 7 numbers = 7 × 10
    ∴ Last number = Sum of 20 numbers – sum of first 12 numbers – sum of next 7 numbers
    Last number = 20 × 12 – 11 × 12 – 7 × 10
    Last number = 240 – 132 – 70 = 38

  1. The average of 15 numbers is 7. If the average of the first 8 numbers be 6.5 and the average of last 8 numbers be 9.5, then the middle number is








  1. View Hint View Answer Discuss in Forum

    Here , Sum of 15 numbers = 15 × 7
    Sum of the first 8 numbers = 8 × 6.5
    and Sum of last 8 numbers = 8 × 9.5
    The middle number = ( Sum of last 8 numbers + Sum of the first 8 numbers ) - Sum of 15 numbers
    The middle number = 8 × 6.5 + 8 × 9.5 – 15 × 7

    Correct Option: C

    Here , Sum of 15 numbers = 15 × 7
    Sum of the first 8 numbers = 8 × 6.5
    and Sum of last 8 numbers = 8 × 9.5
    The middle number = ( Sum of last 8 numbers + Sum of the first 8 numbers ) - Sum of 15 numbers
    The middle number = 8 × 6.5 + 8 × 9.5 – 15 × 7
    The middle number = 52 + 76 – 105
    The middle number = 128 – 105 = 23

  1. The average of prime numbers between 1 and 20 is








  1. View Hint View Answer Discuss in Forum

    Prime numbers between 1 and 20
    ⇒ 2, 3, 5, 7, 11, 13, 17, 19
    Sum = 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19 = 77

    ∴ Required average =
    Sum of given numbers
    Total numbers of terms

    Correct Option: D

    Prime numbers between 1 and 20
    ⇒ 2, 3, 5, 7, 11, 13, 17, 19
    Sum = 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19 = 77

    ∴ Required average =
    Sum of given numbers
    Total numbers of terms

    Required average =
    77
    		 = 9
    5
    88

  1. If the arithmetic mean of 7, 5, 13, x and 9 is 10, then the value of x is :








  1. View Hint View Answer Discuss in Forum

    According to the question,

    Average =
    Sum of given numbers
    Total numbers of terms

    ⇒ 10 =
    7 + 5 + 13 + x + 9
    5

    ⇒ 7 + 5 + 13 + x + 9 = 10 × 5

    Correct Option: D

    According to the question,

    Average =
    Sum of given numbers
    Total numbers of terms

    ⇒ 10 =
    7 + 5 + 13 + x + 9
    5

    ⇒ 7 + 5 + 13 + x + 9 = 10 × 5
    ⇒ 34 + x = 50
    ⇒ x = 50 – 34 = 16

  1. The average of 20 numbers is calculated as 35. It is discovered later on that while calculating the average, one number, namely 85, was mis read as 45. The correct average is :








  1. View Hint View Answer Discuss in Forum

    Here , The average of 20 numbers = 35
    Sum of 20 numbers = 20 × 35
    According to question ,
    Correct sum of 20 numbers = 20 × 35 – 45 + 85
    Correct sum of 20 numbers = 700 + 40 = 740

    Correct Option: C

    Here , The average of 20 numbers = 35
    Sum of 20 numbers = 20 × 35
    According to question ,
    Correct sum of 20 numbers = 20 × 35 – 45 + 85
    Correct sum of 20 numbers = 700 + 40 = 740

    ∴ Required average =
    740
    		 = 37
    20