- #1
roadrunner
- 103
- 0
permutations/combinations help please
Hello everyone im' stuck on this problem.
It says:
Each symbol in braille code is represened by a rectangular arrangement of six dots. Given that a least 1 dot of the 6 must be raised, how many symbols can be represented in brail?
now i saw this posted somewhere else, they got 63. don't know how.
i got 63 two ways...
2^6-1 (case where all down)=63
6c1+6c2+6c3+6c4+6c5+6c6 -1 also =63 (where 6c3 etc is combinations...6 options choose 3)
can sumone explain how/why that works please.
also part b...how many combinations have EXACTLY 3 raised
and how many have an even number of raised dots
Hello everyone im' stuck on this problem.
It says:
Each symbol in braille code is represened by a rectangular arrangement of six dots. Given that a least 1 dot of the 6 must be raised, how many symbols can be represented in brail?
now i saw this posted somewhere else, they got 63. don't know how.
i got 63 two ways...
2^6-1 (case where all down)=63
6c1+6c2+6c3+6c4+6c5+6c6 -1 also =63 (where 6c3 etc is combinations...6 options choose 3)
can sumone explain how/why that works please.
also part b...how many combinations have EXACTLY 3 raised
and how many have an even number of raised dots
Last edited: