Let’s start by calculating the interest earned by Rs. 4,000. We can use the formula for simple interest:

Interest = Principal × Rate × Time

Given that the principal (P) is Rs. 4,000 and the rate (R) is 3% per annum, we need to determine the time (T) in years.

Now, let’s calculate the interest earned by Rs. 4,000 using the formula:

Interest = (4000 × 3 × T) / 100

Simplifying the expression, we get:

Interest = (120T) / 100 Interest = (6T) / 5

Next, let’s calculate the interest earned by Rs. 5,000 over 5 years at a rate of 4% per annum:

Interest = (5000 × 4 × 5) / 100 Interest = 1000

So, we have the equation: (6T) / 5 = 1000

To solve for T, we can cross-multiply and solve for T:

6T = 5 × 1000 6T = 5000 T = 5000 / 6 T ≈ 833.33 years

Therefore, it will take approximately 833.33 years for Rs. 4,000 lent at 3% per annum to earn as much interest as Rs. 5,000 will earn in 5 years at 4% per annum.