Raj borrows ₹ 8,000; out of which ₹ 4,500 at 5% and the remaining at 6%. Find the total interest paid by him in 4 years.

Given:

Total amount Raj borrows = ₹ 8,000

P = ₹ 4,500

R = 5%

T = 4 years

$\because \text{S.I.} = ₹ \Big(\dfrac{P \times R \times T}{100}\Big)\\[1em] \Rightarrow \text{S.I.} = ₹ \Big(\dfrac{4,500 \times 5 \times 4}{100}\Big)\\[1em] \Rightarrow \text{S.I.} = ₹ \dfrac{90,000}{100}\\[1em] \Rightarrow \text{S.I.} = ₹ 900$

Remaining Principal = ₹ (8,000 - 4500) = ₹ 3,500

R = 6%

T = 4 years

$\because \text{S.I.} = ₹ \Big(\dfrac{P \times R \times T}{100}\Big)\\[1em] \Rightarrow \text{S.I.} = ₹ \Big(\dfrac{3,500 \times 6 \times 4}{100}\Big)\\[1em] \Rightarrow \text{S.I.} = ₹ \dfrac{84,000}{100}\\[1em] \Rightarrow \text{S.I.} = ₹ 840$

Total interest paid in 4 years = ₹(900 + 840) = ₹ 1,740

Hence, total interest paid in 4 years = ₹ 1,740.