CAT Difficult Questions

Difficult CAT Questions-Directions for next 2 CAT Questions: Answer the cat questions on the basis of the text given below

There are n urns each containing n + 1 balls such that the ith urn contains i white balls and (n + 1 − i) red balls. Let ui be the event of selecting ith urn, i = 1, 2, 3 …, n and w denotes the event of getting a white ball.

1. If n is even and E denotes the event of choosing even numbered urn ( P(ui) = 1/n) , then the value of P(w/E) is
a) (n+2) / (2n+1)
b) (n+2) / 2(n+1)
c) n / (n+1)
d) 1 / (n+1)
e) none of these
Answer b) (n+2) / 2(n+1)
P( w/E) = (2+4+…+n) / {n(n+1)/2} = (n+2) / 2(n+1)

2. If P(ui) = c, where c is a constant then P(un/w) is equal to
a) 2/ ( n+1)
b) 1/ (n+1)
c) n/(n+1)

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