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Nov 2013 p62 q7
2935
Rory has 10 cards. Four of the cards have a 3 printed on them and six of the cards have a 4 printed on them. He takes three cards at random, without replacement, and adds up the numbers on the cards.
Show that P(the sum of the numbers on the three cards is 11) = \(\frac{1}{2}\).
Draw up a probability distribution table for the sum of the numbers on the three cards.
Solution
(i) To find the probability that the sum of the numbers on the three cards is 11, consider the possible combinations: (3, 4, 4), (4, 3, 4), or (4, 4, 3). The probability for each combination is calculated as follows: