In a survey of 135 pet owners, 52 said they own a dog, and 59 said they own a cat. 15 said they own both a dog and a cat? How many owned a dog but not a cat?
To find out how many owned a dog but not a cat, we need to subtract the number of people who owned both a dog and a cat from the total number of people who owned a dog.
Total number of people who owned a dog = 52
Number of people who owned both a dog and a cat = 15
So, the number of people who owned a dog but not a cat = 52 - 15 = <<52-15=37>>37. Answer: \boxed{37}.