Ring Lardner was one of this country's most popular writers during the $1920 \mathrm{~s}$ and 1930 s. He was also a chronic alcoholic who died prematurely at the age of 48 . The following table lists the life spans of some of Lardner's contemporaries $(38)$. Those in the sample on the left were all problem drinkers; they died, on the average, at age 65 . The 12 (sober) writers on the right tended to live a full 10 years longer. Can it be argued that an increase of that magnitude is statistically significant? Test an appropriate null hypothesis against a one-sided $H_{1}$. Use the $0.05$ level of significance. Note: The pooled sample standard deviation for these two samples is 13.9.