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msmith8754
- Newbie | Next Rank: 10 Posts
- Posts: 6
- Joined: Fri Sep 26, 2008 4:24 pm
Hi,
I have a question on probability. Here is the question
John wrote a phone number and can remember that the number had 7 digits, the digit 1 appeared in last three places and 0 did not appear at all. What is the prob that phone number contains at least 2 prime digits?
Ans: 1 MINUS ( prob of no prime digits + having 1 prime digit)
4 prime digits ( 2,3, 5,7)
4 non prime digits ( 4,6,8,9)
prob of choosing a prime digit = 1/2
4 options of one prime digit
one option of no prime digit with a prob of ( 1/2) to the 4 th power
1 MINUS ( 1/2) to the 4th power + 4*(1/2) to the 4th power
Since there are 4 choices for nonprime, why doesn't this part get multiplied by 4 like one prime digit prob?
Thanks
I have a question on probability. Here is the question
John wrote a phone number and can remember that the number had 7 digits, the digit 1 appeared in last three places and 0 did not appear at all. What is the prob that phone number contains at least 2 prime digits?
Ans: 1 MINUS ( prob of no prime digits + having 1 prime digit)
4 prime digits ( 2,3, 5,7)
4 non prime digits ( 4,6,8,9)
prob of choosing a prime digit = 1/2
4 options of one prime digit
one option of no prime digit with a prob of ( 1/2) to the 4 th power
1 MINUS ( 1/2) to the 4th power + 4*(1/2) to the 4th power
Since there are 4 choices for nonprime, why doesn't this part get multiplied by 4 like one prime digit prob?
Thanks
