A certain sum of money lent at simple interest amounts to ₹1,200 in 2 years and ₹1,600 in 4 years. The rate percent per annum is:

25%

Amount in 2 years = Rs.1200

Amount in 4 years = Rs.1600

S.I in 2 years = 1600 - 1200 = Rs.400

S.I. in 1 year = \(\frac{400}{2}\) = Rs.200

Principal = 1200 - 400 = Rs.800

∴ Rate% = \(\frac{Interest}{Principal}\) × 100 

             = \(\frac{200}{800}\) × 100 = 25%