You don’t need any fancy notation to solve the problem.
You know that $40$% of the candidates are really capable and that $80$% of those $40$% pass the test; $0.8 \cdot 0.4 = 0.32$, so $32$% of all candidates both pass the test and are really capable. Of the remaining $60$% of the candidates, $25$% pass; $0.25 \cdot 0.6 = 0.15$, so $15$% of all candidates both pass the test and aren’t really capable. Altogether, then, $32+15=47$% of the candidates can pass the test, and the fraction of those who are really capable is $32/47$.
Alternatively, you can do as gary suggested and imagine that you’re working with a specific number of candidates. Choose the number so that all of the percentages work out to whole numbers of people; in this case $100$ works. Then you have $40$ who are really capable, of whom $32$ pass, and $60$ who aren’t capable, of whom $15$ pass anyway. Thus, $47$ pass, of whom $32$ are really capable, and the desired proportion is $32/47$. As you can see, this is just doing with specific numbers what I did with the percentages in the previous paragraph.