Precalculus (6th Edition) Blitzer

The probability that a randomly picked American has done less than 4 years of high school or 4 years of high school only is $\frac{85}{174}$.
We know that the probability that a randomly picked American has done less than 4 years of high school or 4 years of high school only is given below: \begin{align} & P\left( \text{less than 4 years of high school} \right)=\frac{(\text{Numbers of students attend of high school less than 4 years)}}{(\text{Total numbers of students)}} \\ & =\frac{29}{174} \\ & P\left( \text{4 years of high school only} \right)=\frac{(\text{Numbers of students completed 4 years of high school)}}{(\text{Total numbers of students)}} \\ & =\frac{56}{174} \end{align} \begin{align} & P\left( \text{less than 4 years of high school or 4 years of high school} \right)=\left[ P\left( \text{less than 4 years of high school} \right)+P\left( \text{4 years of high school only} \right) \right] \\ & =\frac{29}{174}+\frac{56}{\text{174}} \\ & =\frac{85}{174} \end{align} Thus, the probability that a randomly picked American has done less than 4 years of high school or 4 years of high school only is $\frac{85}{174}$.