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排列组合
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A company has assigned a distinct 3-digit code number to each of its 330 employees. Each code number was formed from the digits 2, 3, 4, 5, 6, 7, 8, 9 and no digit appears more than once in any one code number. How many unassigned code numbers are there?
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排列组合
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An analyst will recommend a combination of 3 industrial stocks, 2 transportation stocks, and 2 utility stocks. If the analyst can choose from 5 industrial stocks, 4 transportation stocks, and 3 utility stocks, how many different combinations of 7 stocks are possible?
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排列组合
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From a group of 3 boys and 3 girls, 4 children are to be randomly selected. What is the probability that equal numbers of boys and girls will be selected?
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排列组合
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How many 4-digit positive integers are there in which all 4 digits are even?
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排列组合
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There are 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks. How many possible selections of 4 books from this self include at least one paperback?
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排列组合
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How many different 6-letter sequences are there that consist of 1 A,2 B's,and3 C's ?
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排列组合
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A box contains 10 light bulbs, fewer than half of which are defective. Two bulbs are to be drawn simultaneously from the box. If n of the bulbs in box are defective, what is the value of n?(1)The probability that the two bulbs to be drawn will be defective is $$\frac 1 {15}$$.(2)The probability that one of the bulbs to be drawn will be defective and the other will not be defective is $$\frac 7 {15}$$.
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排列组合
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When tossed, a certain coin has equal probability of landing on either side. If the coin is tossed 3 times, what is the probability that it will land on the same side each time?
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排列组合
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If a certain coin is flipped, the probability that the coin will land heads is $$\frac1 2$$. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?
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排列组合
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A coin that is tossed will land heads or tails, and each outcome has equal probability. What is the probability that the coin will land heads at least once on two tosses?
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排列组合
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If 2 different representatives are to be selected at random from a group of 10 employees and if p is the probability that both representatives selected will be women, is $$p >\frac1 2$$ ?(1)More than $$\frac1 2$$ of the 10 employees are women.(2)The probability that both representatives selected will be men is less than $$\frac1 {10}$$.
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