Number System


  1. The number (10n-1) is divisible by 11 for ?









  1. View Hint View Answer Discuss in Forum

    For even values of n, the number (10n - 1 ) consists of even numbers of nines and hence it will be divisible by 11.

    Correct Option: C

    For even values of n, the number (10n - 1 ) consists of even numbers of nines and hence it will be divisible by 11.


  1. Which of the following numbers is prime ?









  1. View Hint View Answer Discuss in Forum

    119 is divisible by 7, 187 is divisible by 11,247 is divisible by 13 and 551 is divisible by 19. So none of the given numbers is prime.

    Correct Option: D

    119 is divisible by 7, 187 is divisible by 11,247 is divisible by 13 and 551 is divisible by 19. So none of the given numbers is prime.



  1. If in a long division sum,the dividend is 380606 and the successive remainders from the first to the last are 434, 125 and 413, then the divisor is ?









  1. View Hint View Answer Discuss in Forum

    Let d = divisor and q = quotient

    First remove the last remainder:
    d x q + 413 = 380606
    d x q = 380193

    Correct Option: B

    Let d = divisor and q = quotient

    First remove the last remainder:
    d x q + 413 = 380606
    d x q = 380193

    So d cannot be even (choice d) or a multiple of 5 (choice c).

    If we try choice a or b,
    a quick division (by calculator) shows that
    380193 = 451 x 843, the other two choices.

    (In the absence of choices, we could find the prime factors of 380193,
    which are 3 x 11 x 41 x 281 and get various candidate divisors from that.)

    So one of them is the divisor and the other the quotient.

    So we can just check the first remainder:
    843 x 4 = 3372
    3806 - 3372 = 434 ... a match!

    And just to be sure:
    451 x 8 = 3608
    3806 - 3608 = 198

    So the divisor is 843.


  1. A number consists of two digits. The sum of the digit is 10. On reversing the digits of the number, the number decreases by 36. What is the product of the two digits?









  1. View Hint View Answer Discuss in Forum

    Let the unit digits of the number be N and 10s digit be M
    ∴ Number = 10M + N

    According to the question
    MN = 10 .......(i)
    And 10N + M = (10M + N) - 36

    Correct Option: A

    Let the unit digits of the number be N and 10s digit be M
    ∴ Number = 10M + N

    According to the question
    MN = 10 .......(i)
    And 10N + M = (10M + N) - 36
    ⇒ 10N + M - 10M - N = -36
    ⇒ 9N - 9M = - 36
    ⇒ N - M = -4 .......(2)
    On Adding eq. (i) and (ii) we get
    N + M = 10
    N - M = - 4
    2N = 6
    ∴ N = 3 and M = 7
    ∴ Required product of two digits = 3 x 7 = 21



  1. The sum of 5 consecutive odd numbers is 190. What is the sum of the largest and the smallest numbers?









  1. View Hint View Answer Discuss in Forum

    Let the five consecutive number are N - 2, N - 1, N, N +1, N+2
    Sum of numbers = 190
    ∴ N-2 + N -1 + N + N + 2 = 190

    Correct Option: C

    Let the five consecutive number are N - 2, N - 1, N, N +1, N+2
    Sum of numbers = 190
    ∴ N-2 + N -1 + N + N + 2 = 190
    ⇒ 5N = 190
    ∴ N = 38
    Sum of largest and smallest numbers = (N + 2) + (N - 2)
    = 2N = 2 x 38
    = 76