Qualification > Math

Probability

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cashem'up:

--- Quote from: ~Alpha on May 05, 2011, 11:00:28 am ---P (rain) = 3/ 4  :-\

http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9694%20-%20Thinking%20Skills/9694_s07_qp_3.pdf

--- End quote ---

yea exactly that paper... i got as far as this
1. it rains - 3/4 --> Forecast true --> 9/10 = 27/40
2. it doesnt rain - 1/4 --> Forecast false --> 1/10 = 1/40

So probability tht rain is forecasted is 28/40 ??? dont know where I have faltered

Arthur Bon Zavi:

--- Quote from: cashem'up on May 05, 2011, 11:42:00 am ---yea exactly that paper... i got as far as this
1. it rains - 3/4 --> Forecast true --> 9/10 = 27/40
2. it doesnt rain - 1/4 --> Forecast false --> 1/10 = 1/40

So probability tht rain is forecasted is 28/40 ??? dont know where I have faltered

--- End quote ---

No.

(i) - It rains and predicts (3/4 X 9/10) = 27/40

(ii) - It doesn't rain and predicts (1/4 X 9/10) = 9/40

(i) + (ii) : 36/40 = 9/10

cashem'up:

--- Quote from: Fidato on May 05, 2011, 12:11:44 pm ---No.

(i) - It rains and predicts (3/4 X 9/10) = 27/40

(ii) - It doesn't rain and predicts (1/4 X 9/10) = 9/40

(i) + (ii) : 36/40 = 9/10

--- End quote ---

The answer is 13/16 ... how in the world...

Arthur Bon Zavi:

--- Quote from: cashem'up on May 13, 2011, 06:43:32 am ---The answer is 13/16 ... how in the world...

--- End quote ---

CIE doesn't know to make a silly mistake. Leave it.

Alpha:
The answer is good. We just did not study thinking skills. I never even knew about the existence of such a subject.

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