A certain sum of money becomes three times of itself in

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A certain sum of money becomes three times of itself in 20 years at simple interest. In how many years does it become double of itself at the same rate of simple interest ?

Case-I
Let the principal be P
Amount = 3P
∴ Interest = 2P
Time = 20 years

∴ SI =	Principal × Time × Rate
	100

⇒ 2P =	P × R × 20
	100

⇒ R = 10%
Case-II
SI = P
Principle = P
Rate = 10
Time = ?

∴ SI =	Principal × Time × Rate
	100

⇒ P =	P × 10 × T
	100

∴ T = 10 years.
Second method to solve this question :

R% =	(3 - 1)	× 100%
	20

R% = 10%

Now, T =	(n - 1)	year
	R

T =	(2 - 1)	year
	10

T = 10 years