Question

The management of a business concern will be making a decision whether to upgrade their office desktops to Windows 10 from Windows 7. However the management wants to see whether the employees are feeling comfortable in using Windows 10. A one-day training was organized on Windows 10, where all the personnel participated, of whom 20% are secretaries (A). After the seminar a survey was taken. It shows that among secretaries 55% want upgrade to Windows 10 (W10), 17% want no change from Windows 7 (W7), 28% have no preference (NP). Among non-secretarial employees the respective percentages are 39%, 55% and 6%.

If a personnel is selected at random, what is the probability that she is not a secretary, given that she made a definite preference? Answer to 3 digits after decimal.

Answer 1

From the given data, the following Table is calculated:

	Upgrade to Windows 10	No change from Windows 7	No preferences	Total
Secretary	0.20X0.55=0.11	0.20X0.17=0.034	0.20X0.28=0.056	0.20
Not a secretary	0.80X0.39=0.312	0.80X0.55=0.44	0.80X0.06=0.048	0.80
Total	0.422	0.474	0.104	1.00

P(Not a secretary/ Preference) = P(Not a secretary AND Preference)/ P(Preference)

                                           = 0.752/0.896

                                           = 0.839

So,

Answer is:

0.839