In class A, there are 40/100 * 80 = <<40/100*80=32>>32 students.

In class B, the number of students is less by 21, which means class B has 32 - 21 = <<32-21=11>>11 students.

That means 80 - 32 - 11 = <<80-32-11=37>>37 students are in class C.

# Answer

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<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Adam goes to a small school, which teaches 80 students in three classes. 40% of the students are in class A, and class B has 21 students fewer than class A. The rest are in class C. How many students are in this class?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
37
Adam goes to a small school, which teaches 80 students in three classes. 40% of the students are in class A, and class B has 21 students fewer than class A. The rest are in class C. How many students are in this class?
train