Question

# A box contains 5 red and 4 white marbles. Two marbles are drawn successively from the box without replacement and the second drawn marble is found to be white. Probability that the first is also white is? $A.\dfrac{3}{8} \\ B.\dfrac{1}{2} \\ C.\dfrac{1}{3} \\ D.\dfrac{1}{4} \\$

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Hint: Here this is a certain and sure event. Which we will denote by S. This event has a certain number of samples. So, we will first have to calculate and write the samples and then find the probability of each event.

5 red and 4 white marbles are presented by ${R_1},{R_2},{R_3},{R_4},{R_5}$ and ${W_1},{W_2},{W_3},{W_4}$.
$\therefore$Probability of white event = $\dfrac{{no.ofsampleSpaces}}{{TotalNo.ofSpaces}}$
=$\dfrac{3}{8}$
Thus required probability will be $\dfrac{3}{8}$.