Precalculus (6th Edition) Blitzer

The probability that a randomly picked American has done 4 years of high school only or less than 4 years of college is $\frac{50}{87}$.
We know that the probability that a randomly picked American has done 4 years of high school only or less than 4 years of college given below: \begin{align} & P\left( \text{completed 4 years of high school} \right)=\frac{(\text{Numbers of students completed 4 years of high school)}}{(\text{Total numbers of students)}} \\ & =\frac{56}{174} \\ & P\left( \text{less than 4 years college} \right)=\frac{(\text{Numbers of students who attend less than 4 years college)}}{(\text{Total numbers of students)}} \\ & =\frac{44}{174} \end{align} \begin{align} & P\left( \text{4 years of high school or less than 4 years college} \right)=\left[ P\left( \text{completed 4 years of high school} \right)+P\left( \text{less than 4 years college} \right) \right] \\ & =\frac{56}{\text{174}}+\frac{44}{174} \\ & =\frac{100}{174} \\ & =\frac{50}{87} \end{align} Thus, the probability that a randomly picked American has done 4 years of high school only or less than 4 years of college is $\frac{50}{87}$.