In: Statistics and Probability
How many times of “3” are expected to get in rolling an unloaded dice 50 times?
Select one:
a. 25 times
b. 8 times
c. 16.67 times
d. 8.33 times
Let
be a sequence of independent random variables that are all
distributed according to a discrete uniform distribution over the
numbers 1 to 6. These represent our dice rolls.
Now let
be another sequence of variables defined as
That is, the indicators that tell us if the i’th die
roll comesout 3 or not.
Now we have that
and that
This implies that these Y-variables are in fact
Bernoulli distributed with success parameter 1/6. So each Y is 1 if
it’s corresponding die roll yielded 3 and 0 if it didn’t.
Now we can make yet another variable that counts the number of
‘successes’, that is, how many times we get the number 3 in our 50
die rolls. Thus, let
. Now it holds that this sum is binomially distributed with success
parameter 1/6 and number of trials equal to 50.
Hence, we may now calculate the expected number of successes
(i.e. threes) according to the formula for the expectation of the
binomial distribution. That is,
times .
So we see that the number of times we would expect the die to land with 3 up is indeed 8.33 out of 50.
option (d) is correct