If the ratio of two numbers is in the ratio 4 ∶ 9 and their LCM is 720, then find the sum of both the numbers?

  1. 260
  2. 240
  3. 180
  4. 390

Answer (Detailed Solution Below)

Option 1 : 260
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Detailed Solution

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Given:

Ratio of numbers = 4 ∶ 9

LCM of the numbers = 720

 Calculation: 

Let the numbers be 4a and 9a.

∴ Prime factors of 4a = a × 2 × 2

Prime factors of 9a = a × 3 × 3

∴ LCM of 4a and 9a = a × 2 × 2 × 3 × 3

= 36 × a

∵ LCM of 4a and 9a = 720      ------(Given)

∴ 36 × a = 720

⇒ a = 720/36

⇒ a = 20

∴ Numbers are 4a = 4 × 20 = 80

9a = 9 × 20 = 180

∴ Sum of numbers = 180 + 80

= 260

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