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There is an 80% chance David will eat a healthy breakfast and a 25% ch

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Math Expert
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Joined: 02 Sep 2009
Posts: 57237
There is an 80% chance David will eat a healthy breakfast and a 25% ch  [#permalink]

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New post 03 Jan 2019, 11:46
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Difficulty:

  65% (hard)

Question Stats:

38% (01:55) correct 62% (01:08) wrong based on 37 sessions

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There is an 80% chance David will eat a healthy breakfast and a 25% ch  [#permalink]

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New post 04 Jan 2019, 10:14
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There is an 80% chance David will eat a healthy breakfast and a 25% chance that it will rain. If these events are independent, what is the probability that David will eat a healthy breakfast OR that it will rain?

For probability its generally helpful to write this:
For And you must Multiply...
Or you must Add


Using the set formula. We would have to subtract Both the events happening as the question stem asks you the probability for one of the events happening.
Then this becomes easy



P(HB or R) = P(HB) + P(R) - P(HB and R)
= 0.8 + 0.25 - (0.8 x 0.25)
= 0.85
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Re: There is an 80% chance David will eat a healthy breakfast and a 25% ch  [#permalink]

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New post 04 Jan 2019, 12:05
Quote:
For probability its generally helpful to write this:
For And you must Multiply...
Or you must Add

P(A and B) = P(A) * P(B) if, and only if, events A and B are independent.

P(A or B) = P(A) + P(B) if, and only if, P(A and B)=0 [and when A and B are mutually exclusive, it is the case].


These comments are carefully defined, explained and applied in the GMATH method.

Regards,
Fabio.
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Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net
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Re: There is an 80% chance David will eat a healthy breakfast and a 25% ch   [#permalink] 04 Jan 2019, 12:05
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