Carcass wrote:
Three new students are to be assigned at random to 5 empty dormitory rooms. What is the probability that all the three students will be assigned to the same room?
(A) \(\frac{1}{5}\)
(B) \(\frac{1}{10}\)
(C) \(\frac{1}{15}\)
(D) \(\frac{1}{25}\)
(E) \(\frac{1}{30}\)
P(all 3 students assigned to same room) = P(1st student is assigned to ANY room
AND 2nd student assigned to same room as 1st student
AND 3rd student assigned to same room as 1st student)
= P(1st student is assigned to ANY room)
x P(2nd student assigned to same room as 1st student)
x P(3rd student assigned to same room as 1st student)
= 5/5
x 1/5
x 1/5
= 1/25
Answer: D