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In how many ways can one or more of $101$ letters be posted in $101$ letter boxes?

$\quad\quad\quad\quad\quad1)10100 \quad\quad 2) 101^{100} \quad\quad 3) 100^{101} \quad\quad 4) 101(101^{101} - 1)/100$

I am not sure where I am going wrong in interpreting this problem but the obvious thing that came to my mind is to assume letters and letter boxes all distinct and apply mutual inclusion-exclusion but from the answer options that doesn't seems not be the correct approach for this one.where exactly I am going wrong?

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    @Thijs Laarhoven:I don't know the answer yet,but I agree this is not much of good formulation.2011-09-15

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Hint: It appears you are considering all the letters and all the boxes to be distinct, but you post letters in a given order. I can't get any of the answers to work any other way. Then one letter can be posted to one of $101$ boxes in $101$ ways, two letters can be posted in $101^2$ ways (each letter is independent of the other), and so on. Summing the geometric series gives what?

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    @Sri: Boxes and letters are interchangeable here. I interpreted the different alphabet symbols as different mailboxes and position $1$ as the letter to Ross.2011-09-15