- #1
tiger2030
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Homework Statement
How many ways can 5 different letters be posted in 3 boxes, if
any number of letters can be posted in all of the three post boxes?
Homework Equations
Order of the letters being put into the box doesn't matter, only which letter or letters ends up in which box. A box can have 0 letters in the box
The Attempt at a Solution
I tried to break it into cases:
Case 1:
All five letters go into one box
(5C5)(3C1)=1*3=3
Reasoning:Out of the five letters I choose five. Out of the three boxes, I am choosing one to put these letters.
Case 2:
Four letters go into one box, remaining letter into one box
(5C4)(3C1)(1C1)(2C1)=5*3*1*2=30
Reasoning:Out of the five letters I choose four. Out of the three boxes, I am choosing one to put these letters. Then I am choosing the remaining letter. Out of the two boxes left, I am choosing one to put the letter in.
Case 3:
Three letters go into one box, remaining two letters go into one box
(5C3)(3C1)(2C2)(2C1)=10*3*1*2=60
Reasoning:Out of the five letters I choose three. Out of the three boxes, I am choosing one to put these letters. Then I am choosing the remaining letters. Out of the two boxes left, I am choosing one to put the letters in.
Case 4:
Three letters go into one box, one letter goes into second box, one letter goes into third box
(5C3)(3C1)(2C1)(2C1)=10*3*2*2=120
Reasoning:Out of the five letters I choose three. Out of the three boxes, I am choosing one to put these letters. Then I am choosing one of the remaining letters. Out of the two boxes left, I am choosing one to put this letter in.
Case 5:
Two letters go into one box, two letters go into second box, one letter goes into third box
(5C2)(3C1)(3C2)(2C1)=10*3*3*2=180
Reasoning:Out of the five letters I choose two. Out of the three boxes, I am choosing one to put these letters. Then I am choosing two of the remaining letters. Out of the two boxes left, I am choosing one to put these letters in.
Total possibilities equal to the sum of all the cases
3+30+60+120+180=393
If this is not correct, please help to guide me to the correct answer, not simply provide the answer with the work. Thank you for any help.