# Dice probability question

• Mar 23rd 2010, 04:20 PM
Fiah
Dice probability question
I am stuck on this...

Q: If you roll 3 dice, what is the probability that the product of the 3 numbers will be a prime number (1,3,5,7,11,17) ?

Thanks for the help!
• Mar 23rd 2010, 04:41 PM
pickslides
Make a Lattice or Tree diagram and count the results that give a prime.
• Mar 23rd 2010, 05:14 PM
Fiah
I got 5/108 ... does that sound right?
• Mar 23rd 2010, 08:46 PM
mr fantastic
Quote:

Originally Posted by Fiah
I got 5/108 ... does that sound right?

Are there no more that 5 combinations whose product gives a prime number ....? By the way, 1 is not a prime number ... And your list is missing a prime number .... Perhaps your first step should be to review prime numbers.
• Mar 23rd 2010, 09:09 PM
Fiah
In this context, I considered '1' as a prime, I know it is not a true prime number. I did forget to put 2 in my prime number list, my mistake..

...(4/6)(1/6)(1/6) + (1/6)(3/6)(1/6)+ (1/6)(1/6)(3/6)
...4/216 + 3/216 + 3/216
...10/216 (reduce)
...5/108

That's how I got 5/108