If m and n are two positive real numbers such that 9m2 + n2 = 40 and mn = 4, then the value of 3m + n is:

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SSC CGL 2022 Tier-I Official Paper (Held On : 08 Dec 2022 Shift 1)
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  1. 160
  2. 64
  3. 10 
  4. 8

Answer (Detailed Solution Below)

Option 4 : 8
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Detailed Solution

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Given:

9m² + n² = 40

mn = 4

Calculations:

9m² + n² = 40

On adding 6mn both sides, we get:

9m² + n² + 6mn = 40 + 6mn

⇒(3m)² + n² + 2(3m)n = 40 + 6(4)

⇒(3m + n)² = 64

⇒ 3m + n = √64 = 8

Hence, The Required value is 8.

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