The following table summarizes the ages of the 400 richest Americans. Suppose we select one of these individuals. Find the probability that the selected individual is less than 80 years old. 
Definitions:
Probability Sampling
A sampling method where each member of the population has a known, non-zero probability of being selected in the sample.
Sample Proportion
The fraction or percentage of the sample that possesses a certain property or characteristic.
Probability
An indicator of the probability or risk that a certain event will happen, represented by a numerical value ranging from 0 to 1.
Population Mean
The average of a set of numerical values, calculated by summing all the observations and dividing by the total number of observations in the population.
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