Question

if the simple interest on a sum of money at 5%p.a annum for 3 years is rupees 1200 the compound interest for the same sum for the same period at the same rate

Answer 1

s.i= p*r*t/100
so
p= s.i*100/p*r
p=1200*100/5*3
p=8000

c.i= 8000(1+5/100)³-8000
=8000*1.157625-8000
=9261-8000
=1261.

Answer 2

Answer:

Principal = Rs 8000, CI =  Rs 1261

Step-by-step explanation:

S.I = p * r* t/100

t = 3 year

S.I = Rs 1200

r = 5%p.a

1200 = p * 5 * 3/100

1200 * 100/15 = p

p = Rs 8000

Now,

for compound interest

A = p ( 1 + r/100)^t

= 8000 ( 1 + 5/100)^3

= 8000 * 21 * 21 * 21 / 20 * 20 * 20

= 21 * 21 * 21 = 9261

CI = A - P = 9261 - 8000 = Rs 1261