Rupees 4,000 amounts to ₹ 5,000 in 8 years; in what time will ₹ 2,100 amount to ₹ 2,800 at the same rate?

What sum of money lent at 6.5% per annum will produce the same interest in 4 years as ₹ 7,500 produce in 6 years at 5% per annum?

At what rate per cent of simple interest will the interest on ₹ 3,750 be one-fifth of itself in 4 years? What will it amount to in 15 years?

On what date will ₹ 1,950 lent on 5th January, 2011 amount to ₹ 2,125.50 at 5 percent per annum simple interest?