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    ​If the ratio of two numbers is 5 : 3 and the product of their LCM and their HCF is 135, then the sum of the reciprocals of the LCM and the HCF is:​​​
    Question

    ​If the ratio of two numbers is 5 : 3 and the product of their LCM and their HCF is 135, then the sum of the reciprocals of the LCM and the HCF is:​​​

    A.

    1645\frac{16}{45}​​

    B.

    1685\frac{16}{85}​​

    C.

    1661\frac{16}{61}​​

    D.

    1673\frac{16}{73}​​

    Correct option is A

    Given:

    The ratio of the two numbers is 5 : 3

    The product of their LCM and HCF is 135

    Formula Used:

    LCM × HCF = Product of the numbers

    Solution:

    Let the two numbers be 5x and 3x

    The product of the numbers: 

    (5x) × (3x) = 135

    15x= 135

    x2​= 13515\frac{135}{15} = 9 

    x = 3

    The two numbers are 5x = 15 and 3x = 9

    The HCF of 15 and 9 is 3, and the LCM of 15 and 9 is 45

    The sum of the reciprocals of the LCM and HCF:

    1LCM+1HCF\frac{1}{\text{LCM}} + \frac{1}{\text{HCF}}​​

    =145+13= \frac{1}{45} + \frac{1}{3}​​

    =145+1545= \frac{1}{45} + \frac{15}{45}​​

    =1645= \frac{16}{45}​​

    Thus, the sum of the reciprocals of the LCM and HCF = 1645\frac{16}{45}​​

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