Correct Answer - Option 3 : 7.5%
Given:
A lent Rs. 8400 to B for 3 years at simple interest
A lent Rs. 7200 to C for 4 years at simple interest
Received interest = Rs. 4050
Formula Used:
Simple Interest = PRT/100
Where, P = Principal, R = Rate and T = Time
Calculation:
Let the rate of interest be R% per annum
Now, According to the question
Interest paid by B to A = (8400 × R × 3)/100
⇒ Interest paid by B to A = 252R ----(i)
Interest paid by C to A = (7200 × R × 4)/100
⇒ Interest paid by C to A = 288R ----(ii)
On adding equation (i) and equation (ii) we get,
Interest paid by B and C to A = 252R + 288R
⇒ 540R
Now, According to the question
540R = 4050
⇒ R = 7.5
∴ The rate percent per annum is 7.5%