Below is an instruction that describes a task. Write a response that appropriately completes the request in English. Please answer in English.

### Instruction:
A fifth-grade class went on a field trip to the zoo, and their class of 10 students merged with another class with the same amount of students. 5 parents offered to be a chaperone, and 2 of the teachers from both classes will be there too. When the school day was over, the students could choose to go home and 10 of them left. Two of the chaperones were parents in that group, so they left as well. How many individuals were left at the zoo?

### Response:
In total, there were 10*2=<<10*2=20>>20 students.
There were 5 chaperones, 2 teachers, and 20 students, so 5+2+20= <<5+2+20=27>>27 individuals in total.
When the school day ended, 27-10=<<27-10=17>>17 individuals were left.
A couple of chaperones followed suit, leaving 17-2=<<17-2=15>>15 individuals at the zoo.
#### 15