A person invested a sum of Rs. 10,500 at x% per annum at simple interest and a sum of Rs. 13,500 at (x + 2)% p.a. at simple interest. If the total interest earned on both the investments for 3 years is Rs. 7,650, then the rate of interest on the first investment is:

9.5%

We know,

SI = prt/100

According to the question

(10500 × x × 3)/100 + [13500 × (x + 2) × 3]/100

315x + 405x + 810 = 7650

720x = 7650 – 810 = 6840

x = 6840/720 = 9.5%