The odds in favor of Dave selecting a gray t-shirt can be calculated as the number of favorable outcomes (gray t-shirts) divided by the number of total outcomes (all t-shirts):
Number of gray t-shirts = 5
Total number of t-shirts = 16
Odds in favor of gray t-shirt = Number of gray t-shirts / Total number of t-shirts
Odds in favor of gray t-shirt = 5/16
Therefore, the odds in favor of Dave selecting a gray t-shirt are 5/16.