Sunday, March 7, 2010

Spider & Flies

A spider eats 3 flies a day [he eats first 3 flies which get caught in his web.] The probability of a fly getting caught in the web is 50%. Today, 5th fly is passing by that area, what is the probability of its survival ?

3 comments:

Unknown said...

Answer : 0.125

There are 4 possibilities:

1) 3 out of the 4 previous flies have been eaten, in which case the survival chance is 1

2) 2 out of the 4 previous flies have been eaten, in which case the survival chance is 0.5

3) 1 out of the 4 previous flies have been eaten, in which case the survival chance is 0.5

4) none of the previous flies have been eaten, hence survival chance is 0.5

Hence, probability of survival is 1 * 0.5 * 0.5 * 0.5 = 0.125

Mandeep Singh said...

more puzzles

Ishwardeep Singh said...
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