AMC考试练习题及答案解析（3）
Problem
Two dice are thrown. What is the probability that the product of the two numbers is a multiple of 5?
Solution
This is equivalent to asking for the probability that at least one of the numbers is a multiple of 
, since if one of the numbers is a multiple of , then the product with it and another integer is also a multiple of , and if a number is a multiple of , then since is prime, one of the factors must also have a factor of , and is the only multiple of on a die, so one of the numbers rolled must be a . To find the probability of rolling at least one , we can find the probability of not rolling a and subtract that from 
, since you either roll a or not roll a . The probability of not rolling a on either dice is 
. Therefore, the probability of rolling at least one five, and thus rolling two numbers whose product is a multiple of , is 
问题
扔了两个骰子。这两个数的乘积是5的倍数的概率是多少？
解
这相当于要求至少有一个数字是其倍数的概率
，因为如果其中一个数字是倍数，那么带有它的产品和另一个整数也是倍数，如果数字是一个倍数，然后是素数，其中一个因素也必须有一个因子，并且是骰子上的唯一倍数，因此其中一个数字必须是a 。为了找到滚动至少一个的概率，我们可以找到不滚动的概率并从中减去
，因为你要么滚动a 还是不滚动a 。不掷任何一个骰子的概率是
。因此，滚动至少五个的概率，从而滚动两个产品是其倍数的数字，是
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