The simple interest on a sum of money will be Rs. 600 after 10 years. If the principal is tripled after 5 years, what will be total interest at the end of the tenth year? एक धनराशि पर 10 वर्ष के बाद साधारण ब्याज 600 रू. है। यदि मूलधन को 5 वर्ष के बाद तिगुना कर दिया जाये तो 10 वें वर्ष की समाप्ति पर कुल ब्याज क्या होगा?

Let principal = P and rate = r%. Simple interest for 10 years on P is Rs.600, so (P × r × 10)/100 = 600, meaning Pr = 6000. For first 5 years: interest = (P × r × 5)/100 = 3000/100 = Rs.300. Principal triples after 5 years, so new principal = 3P. Next 5 years interest = (3P × r × 5)/100 = 15 × (Pr)/100 = 15 × 6000/100 = Rs.900. Total interest = 300 + 900 = Rs.1200. Option A is correct.