The simple interest on a sum of money will be Rs. 600 after 10 years. If the principal is trebled after 5 years the total interest at the end of 10 years will be?

Let the sum be Rs. P, SI = Rs. 600, Time = 10 years
∴ Rate (600 x 100) / (P x 10)%
S.I for first 5 years = Rs. (P x 5 x 6000)/(1000 x P) = Rs. 300
S.I for last 5 years = Rs. (3P x 5 x 6000)/(100 x P) = Rs. 900
Hence, total interest at the end of 10 years = 300 + 900 = Rs. 1200.