Question

I have an unlimited supply of standard 6-sided dice. What's the fewest number of dice that I have to simultaneously roll to be at least 90% likely to roll at least one 6?

Answer 1

hmmmmmm

Answer 2

the site sucks today ... keeps kicking me out

Answer 3

That's alright, take your time. I just want to make sure I understand this

Answer 4

Ok so basically we are add all the probabilities of landing on a 6 until we reach 90% or .9
So the probability of landing on a 6 is 1/6 do you agree?

Answer 5

Yes, the probability is 1/6 or 0.16666667

Answer 6

So the probability of landing on 6 the first time is 1/6
The probability of landing on 6 a second is 1/6 the probability of landing on a 6 the third is 1/6
So basically is
P(6)=1/6+1/6+1/6 .... = .9
So basically the formula can be arranged as follows
x(1/6)=.9

Solve for x
x represents how many times you roll the die

Do you follow?

Answer 7

Oh ok! I get it

Answer 8

so we then divide 0.9 by 1/6?
Then round up to the nearest whole number?

Answer 9

yup :)

Answer 10

Thanks so much!

Answer 11

Do you get why we added all the probabilities?

Answer 12

Well I understand we do not multiply them, because multiplying them would get us the probability of rolling a 6 each time

Answer 13

So we add them together because we just want one or more 6

Answer 14

yaaaaa :D

Answer 15

Ya get the concept so we are good