A person invested one fourth of the sum of Rs.25000 at a certain rate of simple interest and the rest at 4% p.a. higher rate. If the total interest received for 2 years is Rs.4125, what is the rate at which the second sum was invested?

5.25%

Total interest = \(\frac{25000 × R × 2}{100 × 4}\) + \(\frac{3 × 25000 × (R + 4) × 2}{100 × 4}\) = 4125

⇒ \(\frac{25000 × 2 (R + 3(R +4))}{400}\) = 4125

⇒ 125 (4R + 12) = 4125

⇒ (4R + 12) = 33

⇒ 4R = 21

⇒ R = 5.25