Hi. I know there must be a formula for this question, but I just can't figure it out.
Q.) Imagine a large multiple choice sheet printed with response spaces like the sample below. Now how many unique responses can be encoded? Explain your reasoning!
(A)(B)(C)(D)(E)(F)(G)(H)(I)
well, you can have 9 single answers
and 9*8 double answers
and 9*8*7 triple answers and so on.
It looks as if the sum must be
Sum(9-n)!/(n)! from n=0 to 8
check that.