JEE MAIN - Mathematics (2019 - 10th January Morning Slot - No. 21)
An unbiased coin is tossed. If the outcome is a head then a pair of unbiased dice is rolled and the sum of the numbers obtained on them is noted. If the toss of the coin results in tail then a card from a well-shuffled pack of nine cards numbered 1, 2, 3, ……, 9 is randomly picked and the number on the card is noted. The probability that the noted number is either 7 or 8 is :
$${{19} \over {36}}$$
$${{15} \over {72}}$$
$${{13} \over {36}}$$
$${{19} \over {72}}$$
Explanation
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$$P\left( A \right) = {1 \over 2} \times {{11} \over {36}} + {1 \over 2} \times {2 \over 9} = {{19} \over {72}}$$
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