Question

What sum will amount to Rs. 1320in 2 years at compound interest, if the rates are 10% and 20% for the successive years?

Answer 1

Step-by-step explanation:

C.I. for the third year = Rs. 1,452.

C.I. for the second year = Rs. 1,320

∴ S.I on Rs. 1,320 for one year = Rs. 1,452− Rs. 1,320= Rs. 132.

Rate of interest =

1,320

132×100

=10%.

Let the original money be Rs. P.

Amount after 2 year − amount after one year =C.I. for second year.

P(1+

100

10

)

2

−P(1+

100

10

)=1,320

P[(

100

110

)

2

−

100

110

]=1,320

⇒P[(

10

11

)

2

−

10

11

]=1,320⇒P(

100

121

−

10

11

)= Rs. 1,320

⇒P×

100

11

=Rs.1,320⇒P=

11

1,320×100

= Rs. 12,000

∴ Rate of interest =10%

and Original sum of money = Rs. 12,000