FT stands for Full time, F stands for Female. ∩ stands for Intersect, U stands for Union.
So, P(FT ∩ F) = P(FT) * P(F / FT), in words it means as below,
P(picking a Full time student AND a female student) = P(picking a Full time student) * P(picking a female student GIVEN probability of picking a Full time student)
P(FT ∩ F) = P(FT) * P(F / FT)
= 140/200 * 80/140
= 80/200
= 0.4
Otherwise, we can just use Yide's and the lecturer's method of just taking 80/200 = 0.4 to get the answer straight away from the chart.
iii) P(FT U F) = P(FT) + P(F) - P(FT ∩ F)
P(Full time or Female) = 140/200 + 120/200 - 0.4
= 0.9
Otherwise Yide's and the lecturer's method is just to take (80 + 60 + 40)/200 = 0.9 to get the answer.
JJ, the reason we were wrong was becoz we treated the two probabilites as independent. But i realised that choosing a female when choosing a full time student are not independent of each other.
Sorry JJ, Stamfy, Lye Huat. And ya Yide u are Right. haha.