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标题: [求助]GWD6-9 [打印本页]

作者: bobiouou    时间: 2005-12-16 07:26     标题: [求助]GWD6-9

Q9:If an integer n is to be chosen at random from the integers 1 to 96, inclusive, what is the probability that n(n + 1)(n + 2) will be divisible by 8?

答案是5/8,可是能被8除的n应该是偶数,1~96一共有一半是偶数,所以是1/2。请教大家我算的对不对?


作者: 我是魔鬼    时间: 2005-12-16 20:30

you have to consider this.. n(n + 1)(n + 2)

so if n = 7, 7 (8) (9) is divisible by 8

besides even numbers, you need to count all the odd numbers right before a 8 mulitple

so total even numbers 38 + 12 (those odd number) = 60

60/96 is the answer






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