There are 9 girls and 11 boys on maths team 2 members get chosen for represent the school what is the probability that the 2 will be of the same sex please show me the working out too thank you

Answer 1

there are 20C2 ways to pick two members

there are 9C2 ways to pick two girls , and there are 11C2 ways to pick two boys

the probability of same sex is ...(9C2 + 11C2) / 20C2