probability

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earth@work: Master | Next Rank: 500 Posts; Posts: 248; Joined: Mon Aug 11, 2008 9:51 am; Thanked: 13 times

probability

by earth@work » Fri Oct 10, 2008 3:13 pm

Events E and F are such that P(not E or not F) = 0.25, State whether E and F are mutually exclusive.
The answer is No, cud u let me know how?

2) The probability that a student will pass the final examination in both English and Maths is 0.5 and the probability of passing neither is 0.1. If the probability of passing the English examination is 0.75, what is the probability of passing the Maths examination?

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Source: Beat The GMAT — Problem Solving | Fri Oct 10, 2008 3:13 pm

4meonly: Legendary Member; Posts: 891; Joined: Sat Aug 16, 2008 4:21 am; Thanked: 27 times; Followed by:1 members; GMAT Score:660(

by 4meonly » Sat Oct 11, 2008 1:42 am

2) The probability that a student will pass the final examination in both English and Maths is 0.5 and the probability of passing neither is 0.1. If the probability of passing the English examination is 0.75, what is the probability of passing the Maths examination?

P(E)+P(M)-P(E&M)+P(notE&notM)=1
0,75+x-0,5+0,1=1
x=0,65

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gmatguy16: Master | Next Rank: 500 Posts; Posts: 124; Joined: Thu Aug 23, 2007 5:11 am; Thanked: 2 times

by gmatguy16 » Sat Oct 11, 2008 5:48 am

passing english exam is independent of passing the math exam,isnt it ?
so p(a and b) = p(a) * p(b)
applying that answer is 2/3.
0.1 value seems to be redundant.
some please confirm ?

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gmatguy16: Master | Next Rank: 500 Posts; Posts: 124; Joined: Thu Aug 23, 2007 5:11 am; Thanked: 2 times

by gmatguy16 » Sat Oct 11, 2008 5:56 am

sorry i confirm 4meonly is correct.maybe i confused myself..
probability of passing neither is 0.1
which means probability of passing either english or math = 0.9
p (a or b) = p(a) +p(b) -p(a and b) ..basic rule
0.9 = 0.75+p(m) -0.5
p(m) =0.65

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earth@work: Master | Next Rank: 500 Posts; Posts: 248; Joined: Mon Aug 11, 2008 9:51 am; Thanked: 13 times

by earth@work » Sat Oct 11, 2008 10:20 am

thanks, yes the answer is 0.65

Cud someone help understand the first question as well of mutually exclusive events.

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ab78: Junior | Next Rank: 30 Posts; Posts: 17; Joined: Mon Sep 29, 2008 12:24 pm; Thanked: 1 times

by ab78 » Sat Oct 11, 2008 2:37 pm

P(not E or not F) if were mutually exclusive then it is true that

P(not E)+ P(not F) = 0.25

1-P(E) + 1-P(F) = 0.25

2-0.25 = P(E) + P(F) (exclusive E & F) events. comes out to be greater than 1 . Probability can't be greater than 1 so it s not exclusive. There has to be some intersection between those two events.