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by stubbornp » Sat Oct 18, 2008 10:32 pm
16. What is the probability that events A and B both occur?
(1) The probability that event A occurs is 0.8.
(2) The probability that event B occurs is 0.6.
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by Saffa » Sun Oct 19, 2008 12:12 am
Funny one: Surely the option are only C and E;

I would say 0.6 x 0.8 = 0.42 thus SUFF

IMO C
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by stubbornp » Sun Oct 19, 2008 5:23 pm
its wrong...Any other volunteer??
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by Ian Stewart » Sun Oct 19, 2008 6:50 pm
The answer is E; the probability that *both* occur is only equal to 0.6*0.8 if the two events are independent (and Saffa- 0.6*0.8 is 0.48, not 0.42 :) ). Imagine the following problem:

Pick a random integer between 1 and 5 inclusive.
Let A be "the number is less than or equal to 4"
Let B be "the number is less than or equal to 3"

Clearly the probability that both A and B occur is 0.6, not 0.48.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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by stubbornp » Sun Oct 19, 2008 10:16 pm
Ian Stewart wrote:The answer is E; the probability that *both* occur is only equal to 0.6*0.8 if the two events are independent (and Saffa- 0.6*0.8 is 0.48, not 0.42 :) ). Imagine the following problem:

Pick a random integer between 1 and 5 inclusive.
Let A be "the number is less than or equal to 4"
Let B be "the number is less than or equal to 3"

Clearly the probability that both A and B occur is 0.6, not 0.48.
Awsome explanation....tnx ian...
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