Question

At what rate percent p. a. will a sum of Rs 4000 yield Rs 1324 as compound interest in 3 years?

Answer 1

Answer:

Step-by-step explanation:

Given that principal = Rs.4000

And C I = Rs.1324

Amount = Principal + C.I

A =  4000 + 1324 .

A = Rs. 5324

let the rate of interest = r%.

Given time = 3 years.

A = p×(1 + r/100)n

5324 = 4000(1 + r/100)3

5324/4000 = (1 + r/100)3

1331/1000 = (1 + r/100)3    [ cube root on both sides]

(11 / 10)3 = (1 + r/100)3  

11 / 10 = 1 + r / 100

11 / 10-1 = r / 100.

1 / 10 = r / 100

r = 100/10

∴ r =10%.

Hence the rate of interest is 10%.

Answer 2

Answer:

P = Rs 4000,C.I.=Rs 1324,n =3 years

A=P +I

A= Rs 4000+1324=Rs 5324

A=P(1+r/100)3 ( 3 is raise to the power)

5324=4000(1+r/100)3

5324/4000=(1+r/100)3

1331/1000=(1+r/100)3

(1+r/100)3-1331/1000-(11/10)3

1+r/100=11/10

r/100=11/10-1=1/10

Therefore R = 100/1000=1/10=10%