A manufacturer of cases for sound equipment requires drilling holes for metal screws. The drill bits wear out and must be replaced; there is expense not only in the cost of the bits but also for lost production. Engineers varied the rotation speed of the drill and measured the life- time y of four bits at each of five speeds.
Speed Lifetime
60 4.6
60 3.8
60 4.9
60 4.5
80 4.7
80 5.8
80 5.5
80 5.4
100 5
100 4.5
100 3.2
100 4.8
120 4.1
120 4.5
120 4
120 3.8
140 3.6
140 3
140 3.5
140 3.4
1. Create a scatterplot of the data. Does there appear to be a relation? Does it appear to be linear?
2. Regardless fit a simple linear regression model to the data. What can you say about the fit of the model to the data?
3. Is there any evident outlier 
. Remove this observation and fit the regression model again. Is it improving the model f?