An outbreak of the deadly Ebola virus in 2002 and 2003 killed 91 of the 95 gorillas in 7 home ranges in the Congo. To study the spread of the virus, measure distance by the number of home ranges separating a group of gorillas from the first group infected. Here are data on distance and number of days until deaths began in each later group:
| Distance x |
1 |
4 |
6 |
6 |
6 |
7 |
| Days y |
2 |
20 |
29 |
38 |
44 |
50 |
Find the correlation r between x and y.