Question
A bag contains 4 white , 5 red and 6 blue balls . Three balls are drawn at random from the bag . The probability that all of them are red is :
Answer: Option C
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Let S be the sample space . Them ,
n(S) = number of ways of drawing 3 balls out of 15 = `15_(C_3) = ((15 xx 14 xx 13))/((3 xx 2 xx 1))` = 455
Let E = event of getting all the 3 red balls.
`:.` n(E) = `5_(C_3) = 5_ (C _ 2) = ((5 xx 4))/((2 xx 1))` = 10.
`:.` P(E) = ` (n(E))/(n(S)) = 10/455 = 2/91`
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