Number System


  1. The total number of integers between 100 and 200, which are divisible by both 9 and 6, is :









  1. View Hint View Answer Discuss in Forum

    A number is divisible by 9 and 6 both, if it is divisible by LCM of 9 and 6 i.e., 18.

    Correct Option: B

    A number is divisible by 9 and 6 both, if it is divisible by LCM of 9 and 6 i.e., 18. Hence, the numbers are 108, 126, 144, 162, 180, 198.
    Thus , the total number of integers between 100 and 200 are 6.


  1. The least number, which must be added to 6709 to make it exactly divisible by 9, is









  1. View Hint View Answer Discuss in Forum

    A number is divisible by 9 if the sum of its digits is divisible by 9.
    Here, 6 + 7 + 0 + 9 = 22

    Correct Option: A

    A number is divisible by 9 if the sum of its digits is divisible by 9.
    Here, 6 + 7 + 0 + 9 = 22
    Now, 22 + 5 = 27, which is divisible by 9. Hence 5 must be added to 6709.



  1. How many 3-digit numbers, in all, are divisible by 6 ?









  1. View Hint View Answer Discuss in Forum

    First 3–digit number divisible by 6 = 102
    Last such 3-digit number =996
    ∴ 996 = 102 + (n –1) 6
    ⇒  (n – 1)6 = 996 – 102 = 894

    Correct Option: B

    First 3–digit number divisible by 6 = 102
    Last such 3-digit number =996
    ∴ 996 = 102 + (n –1) 6
    ⇒  (n – 1)6 = 996 – 102 = 894

    ⇒ n – 1 =
    894
    = 149
    6

    ⇒  n = 150
    Hence , required answer is 150.


  1. (49)15 – 1 is exactly divisible by :









  1. View Hint View Answer Discuss in Forum

    As we know that ,
    xn – an is exactly divisible by (x – a) if n is odd.

    Correct Option: D

    As we know that ,
    xn – an is exactly divisible by (x – a) if n is odd.
    ∴ (49)15 – (1 )15 is exactly divisible by 49 – 1 = 48, that is a multiple of 8.
    Hence required answer is 8.



  1. 1
      + 999 +
    692
    × 99 is equal to
    7693









  1. View Hint View Answer Discuss in Forum

    Expression   =
    1
      + 999 +
    692
    × 99
    7693

    Correct Option: B

    Expression   =
    1
      + 999 +
    692
    × 99
    7693

    =
    1
      + 999 × 99 +
    692
    × 99
    7693

    =
    1
      + (1000 − 1) 99 +
    692
    77

    =
    1
      +
    692
    + 99000 − 99
    77

    =
    693
      + 99000 − 99
    7

    Required answer = 99 + 99000 – 99 = 99000