The Interior Department reports annually on the status of the country’s national forests. In a recent survey done in John Muir Woods in California, the Department used a normal curve to describe the age distribution of trees in the forest. The distribution has a mean of 143 years and a standard deviation of 36 years.
a. What percentage of the trees is less than 60 years old?
b. What percentage of the trees is between 160 and 220 years old?
c. Logging is permitted in the forest, but the government bans the cutting of any trees that are more than 75 years old. What percentage of the trees is off limits?
d. Suppose the Interior Department decides to allow the cutting of the youngest 5% of the trees. Under this rule, loggers would be allowed to harvest trees that are up to ____ years old.