A sum of money doubles itself in 20 years at a certain rate of simple interest. How long will it take for this money to triple?

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Patna High Court Mazdoor Official Paper (Held On: 22 Jun, 2025)
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  1. 30 years
  2. 38 years
  3. 41 years
  4. 40 years

Answer (Detailed Solution Below)

Option 4 : 40 years
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Detailed Solution

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Given:

A sum of money doubles itself in 20 years at a certain rate of simple interest.

Formula used:

Simple Interest (SI) = (P × R × T) / 100

Where, P = Principal, R = Rate of Interest, T = Time

Amount (A) = P + SI

Calculation:

In 20 years, the money doubles itself:

⇒ A = 2P

⇒ SI = P

⇒ P = (P × R × 20) / 100

⇒ R = (100 × SI) / (P × T)

⇒ R = (100 × P) / (P × 20)

⇒ R = 5%

Now to calculate how long it takes for the money to triple:

⇒ A = 3P

⇒ SI = 2P

⇒ SI = (P × R × T) / 100

⇒ 2P = (P × 5 × T) / 100

⇒ T = (2P × 100) / (P × 5)

⇒ T = 200 / 5

⇒ T = 40 years

∴ The correct answer is option (4).

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