0 votes 0 votes How many bit strings of length n contains 1)at least 2) at most 3) exactly r 1's Sanjay Sharma asked Mar 9, 2017 Sanjay Sharma 1.6k views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
Best answer 6 votes 6 votes At least r 1's = $ nCr + nC(r+1) + ....... + nCn $ At most r 1's = $ nC0 + nC1 + ....... + nCr $ Exactly r 1's = $ nCr $ rude answered Mar 9, 2017 selected Mar 9, 2017 by Sanjay Sharma rude comment Share Follow See all 0 reply Please log in or register to add a comment.