A cook had 300 carrots in a bucket he was using to cook meals for a restaurant. Before lunch, he had used 2/5 of the carrots. By the end of the day, he had chopped and used 3/5 of the remaining carrots. How many carrots were not used that day? Let's think first. Chain of thought:
Before lunch, the cook had used 2 / 5 * 300 = 120 carrots. The number of remaining carrots after the cook used 2 / 5 of them is 300 - 120 = 180. The cook had used 3 / 5 * 180 = 108 of the remaining carrots by the end of the day. The number of carrots that the cook did not use that day is 180 - 108 = 72.
Therefore, the answer is 72.