00:01
Okay, so to figure out the expected number of times we roll a die, when we are rolling it either 10 times or until a 6 comes up, we'll let x be the number of times we roll the dice.
00:14
So number of rolls, right? and then we'll consider the case where we roll it once all the way up to 10 times.
00:25
So for example, if we are considering the case where we roll the dice just once, the probability of that occurring, is going to be equal to the probability of rolling a six.
00:40
Okay, and that in a six -sided dye is one -sixth.
00:49
Now, the probability of having to roll the dice exactly two times, it's going to be equal to the probability of rolling anything other than a six multiplied by the probability of rolling a six on that second rule, right? and so that's going to be 5 .6 times 1 .6, which is equal to 536.
01:21
And then the probability of getting three rolls exactly.
01:27
Well, that's going to be the case where we roll not a 6 the first time, right, followed by not as 6 for the second rule.
01:37
But the third rule has to be that 6.
01:40
Okay, and when we multiply that out, it's going to be 25 over 200.
01:49
And 16.
01:53
Now there's a pattern forming here, right? so we could imagine this one -sixth being multiplied by five -sixth to the power of zero.
02:03
I could imagine this five -sixth being to the power of one...