Question

The simple interest on a certain sum for Two years is Rs 800, while the compound interest on the same sum for 2 years is Rs 820. Find the sum and the rate of interest.

Answer 1

Simple interest :

Principle × rate × time

P × r × 2 = 800

2pr = 800

P = 400/r

Compound interest :

P(1 + r)² = P + 820

1 + 2r + r² = 1 + 820/P

P = 820/(2r + r²)

Equating the two :

820/(2r + r²) = 400/r

820r = 800r + 400r²

820r - 800r = 400r²

20r = 400r²

20 = 400r

r = 20/400

r = 0.05

P = 400/0.05 = 8000

Rate :

0.05 × 100 = 5%

Principle = 8000

Answer 2

Answer: #FASTEST method #shortcut

Step-by-step explanation: