A man gets a simple interest of Rs.400 on a certain principal at the rate of 5% p.a in two years. Find the compound interest the man will get on twice the principal in two years at the same rate?
Choose the correct answer:	A) s.550	B) s.556	C) s.656	D) s.750	E) s.820
Let the principal be Rs.P   S.I at 5% p.a in 8 years on Rs.P = Rs.400   (P)(8)(5)/100 = 400   P = 4000   C.I on Rs.2P i.e., Rs.8000 at 5% p.a in two years   =8000{ [1 + 5/100]^2 - 1}   = 8000(41/400)   = Rs. 820   Answer:s.820
<result>E</result>
A man gets a simple interest of Rs.400 on a certain principal at the rate of 5% p.a in two years. Find the compound interest the man will get on twice the principal in two years at the same rate?