posted by Neid on .
Mack rolls a 15-sided cube 45 times, what would you predict the probability to be of Mack's rolling a number less than 5?
The concept of a 15 sided cube startles me.
Did you make this question up yourself?
No, it's a question on a 7th grade Skills Review
You are right; there's no way a 15-sided die could be fair. Even if the area of each face is the same, the angles cannot all be equal, since there is no regular 15-hedron.
Perhaps they want us to assume it is possible.
4 out of the 15 sides are less than 5
about 4/15 in each roll
so in each roll the probability of NOT getting less than 5 is 11/15
so the probability of NEVER getting less than 5 is (11/15)^45
so our answer is
1 - (11/15)^45
which is about
1 - 8.7^-7
which is so close to one that you can count on it :)