I know this is old question but i'd like to solve it :)
Answer:
Obviously!! positive is your answer. thanks!!
10 people who build at the same rate can frame a house in 6 days. That means it will take one person
days to finish the house.
Which means that it will take 4 people
days to finish the house.
So, the fractional part of the house 4 people can frame in 3 days will be 
Thus, Option D is the correct answer.
The probability that 4 are chem majors would be 5%