In what duration will a sum of money double itself at 5% per annum simple interest? 

This question was previously asked in
RRB Technician Grade III Official Paper (Held On: 29 Dec, 2024 Shift 3)
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  1. 18 years
  2. 20 years 
  3. 10 years 
  4. 12 years 

Answer (Detailed Solution Below)

Option 2 : 20 years 
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Detailed Solution

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Given:

Rate of interest (R) = 5% per annum

Sum of money doubles itself, so the amount (A) becomes twice the principal (P).

Formula Used:

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

Amount (A) = Principal (P) + Simple Interest (SI)

Calculation:

Since the amount doubles itself, A = 2P

Simple Interest (SI) = A - P

SI = 2P - P

SI = P

Using the formula for simple interest:

SI = (P × R × T) / 100

P = (P × 5 × T) / 100

⇒ 100P = 5PT

⇒ T = 100 / 5

⇒ T = 20

The correct answer is option 2: 20 years

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