Question

In how many ways we can post 4 letters in 3 letter boxes

Answer 1

$/huge/understand/mathfrakpurple{Answer}$

➡️Either the two remaining letters go in one of the three boxes ((31)= 3 ways), or one letter goes into each of two out of the three boxes ( (32)=3 ways). So this case produces 4⋅(3+3)= 24 arrangements. Two open boxes can occur in (42)= 6 ways.

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