I need help with question 2d and 2e from http://www.vcaa.vic.edu.au/Documents/exams/mathematics/2011mmcas2-w.pdf
All of the chocolates produced by machine A and machine B are stored in a large bin. There is an equal number
of chocolates from each machine in the bin.
It is found that if a chocolate, produced by either machine, takes longer than 3 seconds to produce then it can easily be identified by its darker color
e. A chocolate is selected at random from the bin. It is found to have taken longer than 3 seconds to produce.
Find, correct to four decimal places, the probability that it was produced by machine A.