To find the percentage of dogs that became certified service dogs, we can use the formula:
(Number of certified dogs / Total number of dogs) x 100
In this case, the number of certified dogs is 7 and the total number of dogs is 20. Plugging these values into the formula:
(7 / 20) x 100 = 35%
Therefore, 35% of the dogs in the training class became certified service dogs.