The question is about conditional probability.
So, it cannot be an "O" level E.maths simple probability
question.
New Syllabus "O" Add. Maths no longer covers probability.
Conditional Probability is covered in H2 Maths.
---------------------------------------------------------------------------------
Conditional Probability of Getting event A given event B. ie
P(A/B)
Event B = A person is promoted
Event A = The person who is promoted comes from Division X.
Probability that a person is promoted
= P(XP, YP, ZP)
= 2/10 x 2/6 + 2/30 x 2/6 + 2/50 x 2/6
= 23/225
Probability of a person being promoted who is employed in
division X
= P(A/B)
P(XP)
= ------------------
P(XP, YP, ZP)
2/10 x 2/6
= --------------------------------------------
2/10 x 2/6 + 2/30 x 2/6 + 2/50 x
2/6
= 15/23