The rate of interest for the first 2 years is 5% for the

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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 Rs . 1280. What is the principal ?

1. Rs. 2500
2. Rs. 2000
3. Rs. 3200
4. Rs. 2440

Correct Option: B

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
=Rs. 2000