## Thinking Mathematically (6th Edition)

$\displaystyle \frac{7}{10}$
The empirical probability of event $E$ is $P(E)=\displaystyle \frac{observed\ number\ of\ times\ E\ occurs}{total\ number\ of\ observed\ occurrences}$ ----------- The total number of movie goers is : 900+1080+840+180=3000 The observed number of E, a movie goer being between 19 and 24, is: $P(E)=\displaystyle \frac{900}{3000} =\displaystyle \frac{3}{10}$ The probability of this event not occurring, therefore, is: $P($not E$)=1-\displaystyle \frac{3}{10}=\frac{7}{10}$