The total number of students in the high school is .
The probability of the participant is
.
Similarlly .
.
.
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.
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The probability distribution of is
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Graph :
\Graph the probability distribution.
\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
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Graph of the probability distribution is.
\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
.