Chapter 5.1, Problem 94E

Learning. A college language class was chosen for an experiment in learning. Using a list of 50 words, the experiment involved measuring the rate of vocabulary memorization at different times during a continuous 5-hour study session. It was found that the average rate of learning for the entire class was inversely proportional to the time spent studying and was given approximately by

     $V^{\prime }\left(t\right)=\frac{15}{t}1\le t\le 5$

If the average number of words memorized after 1 hour of study was 15 words, what was the average number of words memorized after 4 hours of study for 1 ≤ t ≤ 5? After 4 hours of study? Round answer to the nearest whole number.