91Ó°ÊÓ

A ballet trainer wants to know how many students from each year's class will return the following year so she can prepare what lessons to provide. She's developed a working probability throughout the seasons, where X signifies the number of years a person will learn ballet with the teacher and P(X) denotes the probability of learning for such years.

The combination of a Random Variable's chances of values taken adds up to 1.

Because the total of probability equals 1

$0.10+0.05+0.10+P\left(4\right)+0.30+0.20+0.10=1$

that is, role="math" localid="1648458749075" $P\left(4\right)+0.85=1$

role="math" localid="1648458925787" $P\left(4\right)=1-0.85=0.15$x multiplied with p(x) yields the third column.

that is, $\left(1\right)(0.10)=0.10,\left(2\right)(0.05)=0.10$

The table below is the result of putting in the values of P(4).