1.  The rate of interest for the first 2 years is 5% for the next 3 years is 8% and beyond this. It is 10% per annum. If the simple interest for 8 years is ₹ 1280. What is the principal ?
A. ₹ 2500
B. ₹ 2000
C. ₹ 3200
D. ₹ 2440

Answer: Option B

Explanation:

r1 = 5%,
r2 = 8%,
r3 = 10%,

t1 = 2 years
t2 = 3 years,
t3 = 8 - (2 + 3) = 3 years
∵ Principal = (Interest x 100) / [(r1 x t1) + (r2 x t2) + (r3 x t3 )]

= (1280 x 100) / (5 x 2 + 8 x 3 + 10 x 3)
= 128000/(10 + 24 + 30)
= 128000/64
= ₹ 2000