Final answer:
The ratio of snakes to total reptiles is 3/10.
Step-by-step explanation:
To write the ratio of snakes to total reptiles as a fraction, we need to determine the number of snakes compared to the total number of reptiles. Since the pet store sold 3 snakes for every 7 lizards, we can assume that there were 3 snakes for every 10 reptiles (3 snakes + 7 lizards).
Therefore, the ratio of snakes to total reptiles is 3/10, which is the answer choice (a).