Xavi wants to measure the impact of using water for irrigation on a stream's flow rate. The flow rates both
upstream and downstream of the irrigation point are normally distributed,
For each location, Xavi selects a random time each month and measures the flow rate in liters per second.
After he has 12 samples per location, he will look at the difference (upstream - downstream) in their
sample means
What do we know about the shape of the sampling distribution of WU - ip, and why?