View Full Version : Probablity Again
Confused_111
Oct 22, 2007, 02:15 AM
Hi there this question really stumped me...
A die is rolled three time. The probablity of getting at least one odd number is what? A tree diagram would be too long to do and the lattice might be useful, other than that I have no clue on how to do it.
Thanks
colbtech
Oct 22, 2007, 02:22 AM
Evens? (1:1) Each roll offers the same odds, 3 odd number 3 even numbers.
Confused_111
Oct 22, 2007, 02:30 AM
I'm sorry, I am still a bit lost Iget what your trying to say. Do I cube root it or something.
Thanks
Capuchin
Oct 22, 2007, 02:36 AM
What's the probability of getting no odd numbers? Therefore, what's the probability of getting at least one odd number?
Confused_111
Oct 22, 2007, 02:53 AM
No odd numbers out of the three roles??
Capuchin
Oct 22, 2007, 02:56 AM
Yes, that should be very simple to work out, then you just work out the probability of NOT getting that outcome.
Confused_111
Oct 22, 2007, 03:09 AM
Oh I see, its so simple. Would it be any chance by Pr of 7/8 of getting at least one odd number
terryg752
Oct 22, 2007, 03:16 AM
How not to get any odd number:
Each time : must be from 2, 4, 6
Each time: Number of ways to get even no. = 3
Number of ways to get any number = 6
Each time dice is rolled, probability of even number = 3/6 = 1/2
Probability getting Only even numbers 3 times is (1/2)^3 = 1/8
Probability : At least one odd number: = 1 - 1/8 = 7/8
galactus
Oct 22, 2007, 08:23 AM
Agree with Terry.
By the binomial probability.
\sum_{k=1}^{3}C(3,k)(1/2)^{k}(1/2)^{3-k}=C(3,1)(1/2)^{1}(1/2)^{2}+C(3,2)(1/2)^{2}(1/2)^{1}+C(3,3)(1/2)^{3}(1/2)^{0}=\fbox{7/8}