Re: [計量] 想問幾題計量
: : John wrote a phone number on a note that was later lost. John can
: : remember that the number had 7 digits, the digit "1" appeared in
: : the last three places and "0" did not appear at all. What is the
: : probability that the phone number contains at least two prime digits?
: : a) 15/16
: : b) 11/16
: : c) 11/12
: : d) 1/2
: : e) 5/8
七個數字，後面三個是1, 沒有0
求包含至少兩個質數的機率
0~9 中質數有2 3 5 7, 然後0和1不會再出現了
所以質數出現的機率是 4/8 = 1/2
非質數出現的機率也是 4/8 = 1/2
至少兩個質數的機率 = 1 - (一個質數的機率 + 沒有質數的機率)
沒有質數的機率 = (1/2)^4 = 1/16
一個質數的機率 = (1/2)^4 * 4 (四個質數) = 4/16
1- (1/16+4/16) = 1 - 5/16 = 11/16
答案B
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12/16 01:42, , 1F
12/16 01:42, 1F
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12/16 09:05, , 2F
12/16 09:05, 2F
推
12/16 09:23, , 3F
12/16 09:23, 3F
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12/16 10:09, , 4F
12/16 10:09, 4F
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12/16 10:17, , 5F
12/16 10:17, 5F
推
12/16 11:46, , 6F
12/16 11:46, 6F
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12/16 11:46, , 7F
12/16 11:46, 7F
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