Mary's ticket costs $2/ticket * 1 ticket = $<<2*1=2>>2

Mary's children's tickets cost 3 tickets * $1 = $<<3*1=3>>3

Together the tickets cost $2 + $3 = $<<2+3=5>>5

After paying with a 20-dollar bill, Mary will receive $20 - $5 = $<<20-5=15>>15

# Answer

15
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Mary goes with her 3 children to the circus. Tickets cost $2 for adults and $1 for children. Mary pays with a $20 bill. How much change will she receive?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
15
Mary goes with her 3 children to the circus. Tickets cost $2 for adults and $1 for children. Mary pays with a $20 bill. How much change will she receive?
train