A city has 40% men and 60% women, 50% of the men are smoking, 30% of women are smoking. Find P(smoking woman).
Have you considered drawing a tree diagram? It should make the 1-step calculation very obvious.
P(woman)=0.6
P(if woman, smokes)=0.3
Assume there are 100 people. Then, there are 40 men and 60 women. 30% of these 60 women smoke, out of the total 100. A quick calculation leads to 18 out of the 100 people being female smokers.