Probability Practice Test 1

Question : 37 of 40

Marks: +1, -0

A bag contains 3 red, 4 white and 5 blue balls. All balls are different. Two balls are drawn at random.The probability that they are of different colours is

$47/66$
$10/33$
$5/22$
None of these

Validate

Solution:

We have the following pattern:
I red, white

P_\I = 3 × 4/{^12C_2}

II red, blue

P_\II = 3 × 5/{^12C_2}

III blue, white

P_\III = 4 × 5/{^12C_2}

Since all these cases are exclusive, so the required probability

= (12 + 15 + 20)/{^12C_2}

= (47 × 2)/(12 × 11) = 47/66 .

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