LCM and HCF


  1. The least number, which when divided by 18, 27 and 36 separately leaves remainders 5,14, and 23 respectively, is









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    The difference between the divisor and the corresponding remainder is same in each case
    ie. 18 – 5 = 13, 27 – 14 = 13, 36 – 23 = 13
    ∴ Required number = (LCM of 18, 27, and 36 ) – 13
    LCM of 18, 27, and 36 = 108

    Correct Option: A

    The difference between the divisor and the corresponding remainder is same in each case
    ie. 18 – 5 = 13, 27 – 14 = 13, 36 – 23 = 13
    ∴ Required number = (LCM of 18, 27, and 36 ) – 13
    LCM of 18, 27, and 36 = 108
    Hence , Required number = 108 – 13 = 95


  1. What least number must be subtracted from 1936 so that the resulting number when divided by 9, 10 and 15 will leave in each case the same remainder 7 ?









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    LCM of 9, 10 and 15 = 90
    ⇒ The multiple of 90 are also divisible by 9, 10 or 15.
    ∴ 21 × 90 = 1890 will be divisible by them.
    ∴ Now, 1897 will be the number that will give remainder 7.
    ∴ Required number = 1936 – 1897

    Correct Option: C

    LCM of 9, 10 and 15 = 90
    ⇒ The multiple of 90 are also divisible by 9, 10 or 15.
    ∴ 21 × 90 = 1890 will be divisible by them.
    ∴ Now, 1897 will be the number that will give remainder 7.
    ∴ Required number = 1936 – 1897 = 39



  1. The smallest number, which when divided by 5, 10, 12 and 15, leaves remainder 2 in each case; but when divided by 7 leaves no remainder, is









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    LCM of 5, 10, 12, 15

    ∴ LCM = 2 × 3 × 5 × 2 = 60
    ∴ Number = 60k + 2
    Now, the required number should be divisible by 7.
    Now, 60k + 2 = 7 × 8k + 4k + 2
    If we put k = 3 , (4k + 2) is equal to 14 which is exactly divisible by 7.

    Correct Option: B

    LCM of 5, 10, 12, 15

    ∴ LCM = 2 × 3 × 5 × 2 = 60
    ∴ Number = 60k + 2
    Now, the required number should be divisible by 7.
    Now, 60k + 2 = 7 × 8k + 4k + 2
    If we put k = 3 , (4k + 2) is equal to 14 which is exactly divisible by 7.
    ∴ Required number = 60 × 3 + 2 = 182


  1. Which is the least number which when doubled will be exactly divisible by 12, 18, 21 and 30 ?









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    We have , The LCM of 12, 18, 21, 30

    ∴ LCM = 2 × 3 × 2 × 3 × 7 × 5 = 1260

    Correct Option: C

    We have , The LCM of 12, 18, 21, 30

    ∴ LCM = 2 × 3 × 2 × 3 × 7 × 5 = 1260

    ∴ The required number =
    1260
    = 630
    2



  1. The least multiple of 7, which leaves the remainder 4, when divided by any of 6, 9, 15 and 18, is









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    LCM of 6, 9, 15 and 18

    ∴ LCM = 2 × 3 × 3 × 5 = 90
    ∴ Required number = 90k + 4, which must be a multiple of 7 for some value of k.
    For k = 4,

    Correct Option: D

    LCM of 6, 9, 15 and 18

    ∴ LCM = 2 × 3 × 3 × 5 = 90
    ∴ Required number = 90k + 4, which must be a multiple of 7 for some value of k.
    For k = 4,
    Required Number = 90 × 4 + 4 = 364, which is exactly divisible by 7.