New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    A box contains 20 red and 15 white balls. The

    probability of drawing two balls of the same colour is?
    A 19/77 Correct Answer Incorrect Answer
    B 281/595 Correct Answer Incorrect Answer
    C 1/23 Correct Answer Incorrect Answer
    D 279/595 Correct Answer Incorrect Answer
    E none of these Correct Answer Incorrect Answer

    Solution

    Let S be the sample space. Then, n(S) = number of ways of drawing 2 balls out of 35 = 35C2 = (35 x 34)/(2 x 1) = 595 Let E= event of drawing 2 balls of the same colour n(E) = 20C2 + 15C2 = (20 x 19)/(2 x 1) + (15 x 14)/(2 x 1) = 190 + 91 = 281 Therefore, P(E) = (n(E))/(n(S)) = 281/595 ` `

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