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:

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RRB NTPC Graduate Level CBT-I Official Paper (Held On: 05 Jun, 2025 Shift 1)
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  1. \(\frac{16}{73}\)
  2. \(\frac{16}{85}\)
  3. \(\frac{16}{45}\)
  4. \(\frac{16}{61}\)

Answer (Detailed Solution Below)

Option 3 : \(\frac{16}{45}\)
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Detailed Solution

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Given:

Ratio of two numbers = 5:3

Product of LCM and HCF = 135

Formula used:

LCM × HCF = Product of the numbers

Calculation:

Numbers = 5x and 3x

Product of numbers = 5x × 3x = 15x2

⇒ LCM × HCF = 15x2 = 135

⇒ x2 = 135/15

⇒ x2 = 9

⇒ x = 3

Numbers = 5x = 15, and 3x = 9

LCM of 15 and 9 = 45

HCF of 15 and 9 = 3

Sum of reciprocals of LCM and HCF = (1/LCM) + (1/HCF)

⇒ Sum = (1/45) + (1/3)

⇒ Sum = 16/45

∴ The correct answer is option (3).

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