Mary Sheridan, a reporter for The Washington Post, wrote about a study describing the characteristics of day laborers in the Washington, D.C., area (June 23, 2005, pp. A1, A12). The study, funded by the Ford and Rockefeller Foundations, interviewed 476 day laborers-who are becoming common in the Washington, D.C., area due to increase in construction and immigration-in 2004. The following table provides a percentage distribution for the number of years the day laborers lived in the United States at the time of the interview.
Years in U.S. Percentage
Less than 1 ......... 17
1–2 ............ 30
3–5 ............ 21
6–10 .......... 12
11–20 .......... 13
21 or more ......... 7
Suppose that one of these day laborers is randomly selected.
a. Without using the general addition rule, determine the probability that the day laborer obtained has lived in the United States either between 1 and 20 years, inclusive, or less than 11 years.
b. Obtain the probability in part (a) by using the general addition rule.
c. Which method did you find easier?