Which smallest positive number should be subtracted from each 9 and 13 so that 18 is the third proportion of them?

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SSC CGL 2022 Tier-I Official Paper (Held On : 03 Dec 2022 Shift 3)
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  1. 2
  2. 4
  3. 3
  4. 1

Answer (Detailed Solution Below)

Option 4 : 1
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Detailed Solution

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Given: 

18 is the third proportion.

Concept used:

1. If A : B :: C : D then (B × C) = (A × D)

2. (a - b)2 = a2 - 2ab + b2

Calculation:

Let the smallest positive number be Q.

The proportion becomes (9 - Q) : (13 - Q) : : (13 - Q) : 18.

​According to the question,

(13 - Q)2 = (9 - Q) × 18

⇒ 169 + Q2 - 26Q = 162 - 18Q

⇒ Q2 - 8Q + 7 = 0

⇒ (Q - 7)(Q - 1) = 0

So, the smallest number = Q = 1

∴ The smallest number is 1.

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