gmat prep ds

We don't know how many balls are white or how many or even

Case A:
=====
Both events or mutually exlusive - Means none of the White balls and Even - That is why probability is 0

P(W intersect E) = 0

No enough info to get result

Case B:
========
P(W) - P(E) = 0.2

P(W) + P(E) != 1 because we have other colors

P(E) can be calculated only if you know how many even balls or how many whites - No info

P (W or E) = P(W) + P(E) - P(W and E)

A & B together does not give enough info

and hence E

gace780 wrote:We don't know how many balls are white or how many or even

Case A:
=====
Both events or mutually exlusive - Means none of the White balls and Even - That is why probability is 0

P(W intersect E) = 0

No enough info to get result

Case B:
========
P(W) - P(E) = 0.2

P(W) + P(E) != 1 because we have other colors

P(E) can be calculated only if you know how many even balls or how many whites - No info

P (W or E) = P(W) + P(E) - P(W and E)

A & B together does not give enough info

and hence E

Just confused with small thing.
Why are we saying we cannot calculate even number of balls.
P(Even balls)= 5/10 [2,4,6,8,10].
Plz. tell me where I am wrong

gmats009 yes we do know p even is 1/2 but you also have to realize problem says each of the 25 balls are numbered from 1-10.

Please le3t me know if i am wrong.


from the second statement .

p(w) - p(E) = 0.2

and from the 1st stement p(w)p(E)=0.

(p(W) + p(E))^2 =0.04

this gives p(W)^2 + p(E)^2 ..


(p(W)+ p(E))^2 = p(W)^2 + p(E)^2..


SO IMO C.

OA pls

IMO: E

the answer is E....I chose C when I took the test.

Just for reference, can someone please explain what the opposite is for the probability of getting a white ball or an even number as the question asks?

Isn't it P(not white) + Prob (not even)???

Also, I thought the prob of A or B is just PA + PB...if not, when is this the case?

Thanks!

Q: P(w)+P(E)=?

1. P(w)*P(E)=0

Insufficient, b/c we can't manipulate the equation into P(W)+P(E)

2. P(W)-P(E)=0.2

Insufficient, b/c we can't manipulate the question in to P(W)+P(E)

1+2:

Still insufficient, b/c we can't manipulate the equation into P(E)+P(E).