Question

Manali lent Some amount to shalu at a Certain rate of Compound interest. Interest at the end of 2 years and 3 years was Rs 945 and 1521 Respectively. What was the rate of intereste?​

Answer 1

Given

and

From (i)/(ii) and put (1 + r) = x

Now, (1 + r) = 7/6

r = 1/6 = 16.67%

see the image

Answer 2

Solution :-

Let us assume that, rate of interest is R% per annum and Principal is Rs.P .

So,

→ CI for 2 years = P[{1 + (R/100)}² - 1] = 945

and,

→ CI for 3 years = P[{1 + (R/100)}³ - 1] = 1521

Let us assume that, {1 + (R/100)} = x .

then,

→ (2 year CI / 3 year CI) = (x² - 1) / (x³ - 1) = 945 / 1521

→ (x - 1)(x + 1)/(x - 1)(x² + x + 1) = 105/169

→ (x + 1)/(x² + x + 1) = 105/169

→ 169x + 169 = 105x² + 105x + 105

→ 105x² - 64x - 64 = 0

→ 105x² - 120x + 56x - 64 = 0

→ 15x(7x - 8) + 8(7x - 8) = 0

→ (7x - 8)(15x + 8) = 0

→ x = (8/7) and (-15/8)

taking x = (8/7)

→ 1 + (R/100) = (8/7)

→ (R/100) = (8/7) - 1

→ (R/100) = (1/7)

→ R = (100/7) % (Ans.)

[ when we taken x = (-15/8) rate will be in negative which is not correct . ]

Learn more :-

CI in 2yr is Rs. 1600 and in 3 yrs it will be Rs. 1700. Find the rate of interest.

https://brainly.in/question/32463301

7. Abhishek invested some amount for 3 yrs at rate of 16(2/3)% per annum at Cl. The difference of CI obtained

only on 3r...

https://brainly.in/question/38286271