Simple interest for the sum of ₹ 1500 is ₹ 30 in 4 yr and ₹ 60 in 8 yr. Find the rate of simple interest.

Given, SI₂ = 60, SI₁ = 30, T₁ = 4 yr, T₂ = 8 yr
According to the question,
[(1500 x R x 8)/100] - [(1500 x R x 4)/100] = 60 - 30
⇒ (6000 x R)/100 = 30
∴ R = 30/60 = 1/2 = 0.5%