This question was previously asked in

UP TGT Mathematics 2021 Official Paper

- 10 years
- 15 years
- 7 years
- 20 years

Option 2 : 15 years

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Formula:

A = P(1 + r/100)n

Where,

A → Amount

P → Principal

r → Rate of compound interest

n → time

Concept:

Let principal be P and rate be r

Amount in 5 years = 2P

A = P(1 + r/100)n

⇒ 2P = P(1 + r/100)^{5}

⇒ 2 = (1 + r/100)^{5}

Now, Cubing both the side

2^{3} = (1 + r/100)5 × 3

⇒ 8 P = P(1 + r/100)15

**∴ The sum will become 8 times of itself in 15 years**

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