Find this Probability problem hard--Help!!

[dddanny2006]

In a certain corporation, there are 300 male employees and 100 female employees. It is known that 20% of the male employees have advanced degrees and 40% of the females have advanced degrees. If one of the 400 employees is chosen at random, what is the probability this employee has an advanced degree or is female?

A)1/20
B)1/10
C)1/5
D)2/5
E)3/4

ANSWER-D Source-Magoosh

I did it this way- P(Advanced degree) OR P(Female)
(100/400)+(100/400) =1/2

I have not been able to apply the Manhattan Concepts in this problem.Im finding probability difficult,please advice on going about it.

Thanks

[ashleysco2006]

How I went about it:

P(Advance Degree) + P(Female) - P(Advance Degree+Female) =
(100/400) + (100/400) - (40/400) =
(5/20) + (5/20) - (2/20) =
(2/5)

If you don't subtract by P(Advance Degree + Female) then you're essentially counting the same thing twice.

Hope that helps.

[RonPurewal]

How I went about it:

P(Advance Degree) + P(Female) - P(Advance Degree+Female) =
(100/400) + (100/400) - (40/400) =
(5/20) + (5/20) - (2/20) =
(2/5)

If you don't subtract by P(Advance Degree + Female) then you're essentially counting the same thing twice.

Hope that helps.

That's pretty much it.

[dddanny2006]

Ron,Im having problems in identifying Disjoint and Independent cases in difficult questions.Where do I look for the disjoint/independent/dependent nature of the problem?Is it in the last part where they ask us what Probability they need?

That's pretty much it.

[RonPurewal]

You don't need the concept of "independence". That has never been tested by GMAC.

"Disjoint" just means that two things can't both happen. I.e., "boy" and "girl" can't both happen (so you can just add the corresponding numbers). "Boy" and "has long hair" CAN both happen (so you can't).
Forget the terminology -- 99% of the difficulty here is caused by the fact that you're taking an easy concept ("can't both happen") and replacing it with a weird, non-intuitive "vocabulary word".


Also, the problem in this thread is not like anything that you'd see on the GMAT.
On the GMAT, you might see an overlapping sets problem (male/female, degree/no degree), OR you might see a probability problem. But you're not going to see a problem with non-trivial elements of both.