Is it .1?
Range = max prob - min prob.
P(A or B) >= P(A)
P(A or B) >= P(B)
Editing..am still debating how to approach this pblm
0.5 <= P(A or B) <= 0.9
Range of P(A or B) = 0.4
I guess, my initial approach was in line with sdasar's explanation below:
maximize P(A or B)
P(A or B) = P(A) + P(B) - P(A&B)
for max prob => P(A&B) = 0 ( A and B are mutually exclusive)
=> 0.9
neither = 0.1
minimize p(A or B) = p(A) + p(B) - P(A&B)
p(A&B) = p(A)*P(B) for independent events
= 0.5*0.4 = 0.2
p(A or B) = 0.7
neither = 0.3
Range = 0.3-0.1 = 0.2
Last edited by GMAT-HELP; 05-13-2006 at 09:05 PM.
The other way of doing is
When A & b are mutually independent events:
The probability that A won't happen is 0.5
The probability that B won't happen is 0.6
Probability that both events (neither A nor B) happen is 0.3
When A & B are mutually dependent(exclusive) events:
The probbality that either A or either B happen is 0.9 and none of them happen is 0.1
The range is 0.2
GMAT-HELP,
0.3 and 0.1 refers to well defined populations. One probablity refers to truly independent random events and the other to truly mutually exclusive events.
If there is any bias between events A and B as you eluded, all bets are off. I don't think the problem (based on the answers) is implying anything other than the above scenarios.
Thanks,
sdasar
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