Carcass wrote:
In how many ways can we put 4 different balls in 3 different boxes when any box can contain any number of balls?
A. 80
B. 81
C. 64
D. 63
E. 82
Take the task of distributing the 4 different balls and break it into
stages.
Stage 1: Select a box for the 1st ball to go into.
There are 3 available boxes, so we can complete stage 1 in
3 ways
Stage 2: Select a box for the 2nd ball to go into.
There are 3 available boxes, so we can complete stage 2 in
3 ways
Stage 3: Select a box for the 3rd ball to go into.
There are 3 available boxes, so we can complete stage 3 in
3 ways
Stage 4: Select a box for the 4th ball to go into.
There are 3 available boxes, so we can complete stage 4 in
3 ways
By the Fundamental Counting Principle (FCP), we can complete all 4 stages (and thus distribute all 4 balls) in
(3)(3)(3)(3)(4) ways (= 81 ways)
Answer: B