Question
A box contains 10 block and 10 white balls. The probability of drawing two balls of the same colour is :
Answer: Option A
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Total number of balls = 20
Let S be the sample space . Then ,
n(S) = number of ways of drawing 2 balls out of 20
= `20_(C_2) = ((20 xx 19))/((2 xx 1))` = 190.
Let E = event of drawing 2 balls of the same colour .
n(E) = `(10_(C_2) + 10_ (C_2)) = 2 xx ((10 xx 9)/(2 xx 1))` = 90.
`:.` P(E) = ` (n(E))/(n(S)) = 90/190 = 9/19`
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