Re: ISI 2015 PEA Answer Key

Posted by deepti on May 06, 2015; 3:18am
URL: http://discussion-forum.276.s1.nabble.com/ISI-2015-PEA-Answer-Key-tp7596538p7596612.html

So d should be the final ans.?? Of question 21

On May 6, 2015 7:40 AM, "Rajat [via Discussion forum]" <[hidden email]> wrote:

For q.7 put x+2y = a and x-2y = b
solve these simultaneous equations to get x and y in terms of a and b. This will give you f(a,b)

Q.21
P(A intersection B) may be zero or non-zero
=> P(A|B) may be zero or non-zero. If it is zero, it is definitely < P(A) because P(A) is non-zero ALWAYS.
Similar argument can be made for P(A|B)<P(B) (only those times when P(A|B) = 0)

so a,c can be ruled out.

now, P(A) = P(A|B) + P(A|B')
=> P(A|B) = P(A) - P(A|B') which obviously is =<P(A)
P(A|B) will be equal to P(A) if P(A|B') = 0. This can happen when A and B are mutually exclusive exhaustive events.
So, we cannot be sure that P(A|B) will only be 'LESS' than P(A) always. They can also be equal

Hope this helps !

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