A random sample of homeowners from Dallas and Houston was asked to identify the primary source of heat for their homes. The following contingency table shows these results.
| Source of Heat |
Dallas |
Houston |
| Natural Gas |
160 |
105 |
| Eletricity |
115 |
45 |
| Oil |
20 |
10 |
| Propane |
15 |
10 |
| Other |
5 |
15 |
Given that the primary source of heat is natural gas, determine the probability that a randomly selected home from this sample is located in Houston.