Given,
Some couples participated in a mixed doubles badminton tournament. If the number of matches played, so that no couple played in a match, is 840,
Now Let total number of persons be 2n, so number of couples will be n
Now number of matches played, so that no couple played in a match is given by,
⇒C2n⋅C2n−2⋅2=840
{as if we choose couple as A,B and other couple as C,D and taking other two couple as {x,y}&{w,z}, so the possible combination of the match where no couple played in a match will be, {A,x}\rightarrow {C,w}&{C,x}\rightarrow {A,w}, hence there are two possible combination after choosing }
⇒n(n−1)(n−2)(n−3)=5⋅6⋅7⋅8
So, n=8
Hence, the number of persons will be, 2n=16