A company found that the man-hours required to manufacture X parts are directly proportional to the square root of X. If it takes 3 man-hours to produce 20 parts, how many man-hours does it take to produce 40 parts?

Answer: According to the meaning of the topic, you can set the square root of 3 =k*20, so obviously the square root of k*40 is the man-hour required to produce 40 parts. And the square root of k*40 is the root number 2 of 3.