The question is in how many ways can 5 letters be mailed if there are 2 mail boxes available? I would say that there are 2 ways to put the first letter (either to Box 1 or Box 2) and there are also 2 ways to put the second letter, etc. so the total number of ways is $2^{5}=32$ but my textbook says the answer is $25$ which is $5^{2}$, the other way round. Who is right?
EDIT: Maybe their answer $25$ does not come from $5^{2}$ but $2^{5}-7$ and I simply forgot to subtract some extraneous ways?