In a stack of cards numbered from 1 to 2o, if a cards are drawn at a random, one after the other without replacement. How many ways can the draw be made so that the number on the second card shows a number greater than 1st?
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What combinations of two cards are possible to total 8?
(first card, second card):
(6,2) (2,6) (5,3) (3,5) (4,4) – only 5 possible scenarios for sum to be 8. One from this 5 has already happened. Notice here that the case of (6,2) is different from (2,6), and similarly the case of (5,3) is different from (3,5).
From this five cases, only in two we have 5. So, the probability is 2 chances out of 5 that the one that occurred had 5: P=2/5.
Answer: D.
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