Question 478671
Total Students = 40
Male =23
Female=(40-23)=17

Selecting 2 students out of 40 = nCr
=40C2
=40!/(40-2)! 2! 
=40*39*38!/38! 2!
=40*39/ 2!
=20*39
=780 ways

Selecting 2 female out of 17 = nCr
=17C2
=17!/(17-2)!2!
=17*16*15!/(15)!2!
=17*16/2
=17*8
=136 ways

P(2 selected students are female)=136/780
P(2 selected students are female)=0.1743