Activity 3: SLR for Quakes
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*Authors*:

Recall the last question from homework 1: would you expect a relationship between 
the magnitude of an earthquake and the number of stations that detect it?

1. Create a plot of the relationship between these two variables.  How would you 
characterize the relationship?

2. Before you go ahead and fit a linear model to this trend, if in fact there 
was *no relationship* between the two, what would you expect the slope to be?
What about the intercept?

3. Ok, now go ahead and fit a linear model to trend and add that line to the plot
from #1. Interpret your slope and intercept in the context of the problem.

4. Verify the way that `lm()` has computed your slope correctly by using R
to do the calculation using the equation we derived at the beginning of class.

5. How many stations do you predict would be able to detect an earthquake of 
magnitude 7.0?

* * *

### Inference for SLR

6. Using R, calculate a 95% confidence interval for the slope of the model that you 
fit in exercise 3.  Confirm the calculation using `confint()`.

7. Interpret the CI for the slope in the context of the problem.
