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 ?
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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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