S.I. = Rs. (15500 - 12500) = Rs. 3000.

Rate =		100 x 3000	%	= 6%
		12500 x 4

Let the sum be Rs. 100. Then,

S.I. for first 6 months = Rs.		100 x 10 x 1		= Rs. 5
		100 x 2

S.I. for last 6 months = Rs.		105 x 10 x 1		= Rs. 5.25
		100 x 2

So, amount at the end of 1 year = Rs. (100 + 5 + 5.25) = Rs. 110.25

 Effective rate = (110.25 - 100) = 10.25%

Let the rate be R% p.a.

Then,		5000 x R x 2		+		3000 x R x 4		= 2200.
		100				100

 100R + 120R = 2200

R =		2200		= 10.
		220

 Rate = 10%.

Let the original rate be R%. Then, new rate = (2R)%.

Note:
Here, original rate is for 1 year(s); the new rate is for only 4 months i.e.  year(s).

		725 x R x 1		+		362.50 x 2R x 1		= 33.50
		100				100 x 3

 (2175 + 725) R = 33.50 x 100 x 3

 (2175 + 725) R = 10050

 (2900)R = 10050

R =	10050	= 3.46
	2900

 Original rate = 3.46%