A telephone manufacturer finds that the life span of its telephones are normally distribute, with a mean of 6.2 years and a standard deviation of 0.5 year. (a) what percent of its telephones will at least 7.25 years? _____%

(b) what percent of its telephones will last between 5.8 years and 6.8 years?_____%

(c) What percent of its telephones will last less

than 6.9 years? ______%