问一道数学题~

jessiecg · 发表于 2010-12-30 08:17:10

Six cards numbered from 1 to 6 are placed in an empty bowl.First one card is drawn and then put back into the bowl; then a second card is drawn.If the cards are drawn at random and if the sum of the numbers on the cards is 8, what is the probability that one of the two cards drawn is numbered 5 ?
A.1/6
B.1/5
C.1/3
D.2/5
E.2/3
答案是D，不太懂，请大家指教~

sdcar2010 · 发表于 2010-12-30 08:25:18

x + y = 8. Both x and y are chosen from the group of 1, 2, 3, 4, 5, 6. What is the probability that either x or y is 5?

6+2 = 5+ 3 = 4 + 4 = 8
So we have 5 total scenarios: (6, 2), (2, 6), (5, 3), (3, 5), and (4,4).

The probability that either x or y is 5 = 2/5.

jessiecg · 发表于 2010-12-30 09:00:07

明白了~好清楚啊。。谢谢~

问一道数学题~

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