Originally Posted by

**lost1** Basicaly the Q is:

30% use Mac, 50% use Windows, 20% use Linux.

Also 60% of mac has virus, 80% of Windows has virus, 10% Linux has virus.

A random computer is chosen and is found to have virus. What is the probability that this computer is a Windows PC?

To a similar question my tutor recomended drawing up a table so I did that for this question as well but cant get the right answer.

| Virus | Non-Virus | TOTAL

Mac | 0.3*0.6= 0.18 | 0.3-0.18=0.12 | 0.3

Windows | 0.5*0.8= 0.4 | 0.5-0.4 =0.1 | 0.5

Linux | 0.2*0.1= 0.02 | 0.2-0.02 =0.18| 0.2

TOTAL | 0.6 | 0.4 | 1

I would have thought the answer is 0.4 but its 2/3 =S

Can someone please point out where iv gone wrong?

Thanks

Sorry didnt know how to make a table and the extra spaces i tried to use dont seem to work...but you get the idea

thanks