A sum doubles itself in 16 years, then in how many years

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A sum doubles itself in 16 years, then in how many years will it triple itself; rate of interest being simple

Let Principal = Rs. p and Simple Interest = Rs. p

Rate =	SI × 100
	Principal × Time

Rate =	p × 100	=	25	% per annum
	p × 16		4

Case II,
Interest = Rs. 2p

∴ Time =	SI × 100
	Principal × Rate

Time =	2p × 100 × 4	= 32 year.
	p × 25

Second method to solve this question :
Here , n = 2

R =	(n - 1)	× 100%
	T

R =	(2 - 1)	× 100
	16

R =	25	%
	4

R = 6	1	%
	4

Now, T =	(n - 1)	× 100
	R

Here , n = 3

T =	(3 - 1)	× 100
	( 25/4 )

T =	800	= 32 years.
	25