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# There are two lines of defence against an attacking

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Intern
Joined: 12 Dec 2004
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There are two lines of defence against an attacking  [#permalink]  04 Jan 2005, 11:02
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There are two lines of defence against an attacking
aircraft. 1st is missile and 2nd is anti-aircraft gun.
the respective prob. that the aircraft being hit by
the missile and the gun are 2/9 and 1/8 respcly.
what is the prob. of hitting the aircraft?
VP
Joined: 30 Sep 2004
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Location: Germany
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...hit by the gun and / or the missile:

2/9 + 1/8 - 2/9 *1/8 = 23/72
VP
Joined: 18 Nov 2004
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p(e) = p(m) + p (g) - p(g and m) = 2/9 + 1/8 - 2/72 = 23/72
Senior Manager
Joined: 30 Dec 2004
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Location: California
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Stupid question: Why do you subtract the product of the probabilities?
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"No! Try not. Do. Or do not. There is no try.

Director
Joined: 31 Aug 2004
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In case of a destruction by the missile, there is no way to destroy one more time the plane with the gun...
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