First slide
Permutations
Question

The number of ways in which n distinct objects can be put into two different boxes so that no box remains empty, is

Moderate
Solution

Each object can be put either in box B1 (say) or in

box B2 (say). So, there are two choices for each of then objects. 

Therefore, the number of choices for n distinct objects is

2×2××2=2n

These choices correspond to either the first or the second box

being empty. Thus, there are 2n2 ways in which neither box is empty.

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