0 votes 0 votes A student has to answer $9$ out of $12$ questions. How many ways if he has to answer at least $4$ out of first $5$ questions? Probability quantitative-aptitude probability + – JeetRoy asked Apr 6, 2018 • retagged Apr 7, 2018 by Subarna Das JeetRoy 1.9k views answer comment Share Follow See 1 comment See all 1 1 comment reply Mk Utkarsh commented Apr 9, 2018 reply Follow Share this question is not related to probability 0 votes 0 votes Please log in or register to add a comment.
Best answer 6 votes 6 votes At least 4 out of first 5 means 4, or 5 out of first 5 questions (so 5, and 4 question out of next 7). $ _{4}^{5}\textrm{C} *_{5}^{7}\textrm{C} + _{5}^{5}\textrm{C} * _{4}^{7}\textrm{C} $ $=5*21 + 1*35$ $= 105 + 35$ $=140$ pankaj_vir answered Apr 6, 2018 • selected Apr 6, 2018 by srestha pankaj_vir comment Share Follow See all 7 Comments See all 7 7 Comments reply Show 4 previous comments JeetRoy commented Apr 6, 2018 reply Follow Share Gr8, may be I have the old version. Thanks for the solution 0 votes 0 votes pankaj_vir commented Apr 6, 2018 reply Follow Share ok 0 votes 0 votes aditi19 commented Aug 12, 2018 reply Follow Share 140 will be correct as in the question it is mentioned that at least 4 out of first 5 have to be chosen. so there are two cases-either choose 4 out of first 5 or choose all first 5 0 votes 0 votes Please log in or register to add a comment.
