The total number of students in the high school is
.
The probability of the participant
is
.
Similarlly
.
.
.
.
.
.
.
The probability distribution of
is
Days , ![]() | \
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Graph :
\Graph the probability distribution.
\.gif\")
The mean value is
.


.
The mean value is
.
The students ate breakfast an average of
days a week.
The variance of random variable
is
.


The variance is
.
The standard deviation is
.
Substitute
.
.
Therefore, the standard deviation is
.
The probability distribution of
is
Days , ![]() | \
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Graph of the probability distribution is.
\.gif\")
The mean value of a random variable
is
.
The students ate breakfast an average of
days a week.
The variance of a random variable
is
.
The standard deviation of a random variable
is
.