A bag contains 5 red, 4 blue and M green
balls if the probability of getting both the balls
green, when two balls are selected at
random is 1/7, find M  Choose the correct choice from the following:
A) 1 B) 2 C) 3 D) 4 E) 5
mC2/m+9C2=1/7   on solving   (m! / (m-2! * 2!) ) / (m+9! / (m+7! * 2!) ) =1/7 From nCr=n! / r!*(n-r)!   on solving   (m! / (m-2)! ) * ( (n-7)! / (n+7)!) =1/7   after solving and cross multiplication   m^2+4m-12=0   on solving   m=2,-6   so m will be 2.   ANSWER:2
<result>B</result>
A bag contains 5 red, 4 blue and M green
balls if the probability of getting both the balls
green, when two balls are selected at
random is 1/7, find M