Solve the conditional probability question

[chwala]

Homework Statement

see attached problem below;

Relevant Equations

conditional probability

My question is on part $c$ of the problem.
Kindly see attached question,...is the second approach correct?

 

[chwala]

my attempt...why is the second approach wrong for question $c$?or is it also correct?

 

[chwala]

i got a little mixed up, but that's the beauty of maths ...the correct solution is
$P(B/A^{'})$=$\frac {3}{5}$

 

[chwala]

i think its now clear...phew!