If it takes 10 people 10 days to shovel 10,000 pounds of coal, how many days will it take half of these ten people to shovel 40,000 pounds of coal? Let's think first. Chain of thought:
The 10 people shovel 10,000 pounds per 10 days, or 10,000 / 10 = 1000 pounds per day per 10 people. And 1000 pounds per day per 10 people is 1000 / 10 = 100 pounds per day per person. Half of ten people is 10 / 2 = 5 people. At 100 pounds per day per person, 5 people can shovel 5 * 100 = 500 pounds per day. Therefore, for 5 people to shovel 40,000 pounds, it will take 40,000 / 500 = 80 days.
Therefore, the answer is 80.