One-third of all the kids are girls, which means 1/3 * 45 = <<1/3*45=15>>15 children.

So there are 45 - 15 = <<45-15=30>>30 boys in the classroom.

# Answer

30
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
There are 45 children in a classroom. One-third of them are girls. How many boys are in the classroom?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
30
There are 45 children in a classroom. One-third of them are girls. How many boys are in the classroom?
train