Question

N a second grade class containing 12 girls and 11 boys, 2 students are selected at random to give out the math papers. what is the probability that both are girls?

Answer 1

`\displaystyle |\Omega|=\binom{23}{2}=(23!)/(2!21!)=(22\cdot23)/(2)=253\\ |A|=\binom{12}{2}=(12!)/(2!10!)=(11\cdot12)/(2)=66\\\\ P(A)=(66)/(253)=(6)/(23)`