Final answer:
12 carpenters can build 240 doghouses in 20 days.
Step-by-step explanation:
To find how many doghouses 12 carpenters can build in 20 days, we first need to find out how many doghouses 1 carpenter can build in 20 days. Since 1 carpenter can build 1 doghouse in 1 day, they can build 20 doghouses in 20 days. Therefore, 12 carpenters can build 12 times as many doghouses, which is 12 * 20 = 240 doghouses in 20 days.