Question

If a certain sum of money doubles itself in 20 years at a certain rate %, how many times will it become in (a) 40 years (b) 30 years ?​

Answer 1

Step-by-step explanation:

Let the principal be x

Amount after 15 years = 2x

Principal + simple interest = 2x

⇒ x + simple interest = 2x

⇒ Simple interest = x

⇒ (Principal × rate × time)/100 = x

⇒ (x × rate × 15)/100 = x

⇒ Rate = 100/15 = (20/3)%

Now,

Amount = 5x

⇒ Principal + simple interest = 5x

⇒ x + simple interest = 5x

⇒ Simple interest = 4x

⇒ (Principal × rate × time)/100 = 4x

⇒ {x × (20/3) × time}/100 = 4x

∴ Time = 60 years

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