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January 4th, 2015, 12:31 PM   #1
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Need help again...

Hello again,
sorry for asking for too much, but I'm facing problems again... The task goes like this:
There are 18 archers. 5 of them hit the target with the probability 0,8;
7 with the probability 0,7; 4 with the probability 0,6 and 2 with the probability 0,5.
A randomly picked archer shot, but missed the target. What is the probability that he belonged to the group of archers who have the probability of 0,7 of hitting the target?
THE CORRECT ANSWER IS 7/19.
I thought it was 7/18, but I was wrong.
Does someone know how to get the right answer?
Thank you for the help!

Last edited by skipjack; January 4th, 2015 at 02:12 PM.
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January 4th, 2015, 02:09 PM   #2
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7*(1 - 0.7)/(5*(1 - 0.8) + 7*(1 - 0.7) + 4*(1 - 0.6) + 2*(1 - 0.5)) = 7/19
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January 4th, 2015, 09:26 PM   #3
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Thank you very much!
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