Let x be the number of $10 bills.

So, there are (x + 1) $20 bills.

Adding the $10 and $20 bills should sum up to $80 so the equation is 10x + 20(x + 1) = 80.

Then, distribute 20 to x + 1 so it becomes 10x + 20x + 20 = 80.

Combining the like terms on the left side gives 30x + 20 = 80.

Then transfer 20 to the right side of the equation, so it becomes 30x = 60.

To solve for x, we have 60/30 = <<60/30=2>>2.

Therefore, there are 2 $10 bills.

# Answer

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<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Viggo spent $80 on a shirt. He paid the shirt using $20 and $10 bills. If she gave the clerk one more $20 bill than $10 bills, how many $10 bills did he give?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
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user
2
Viggo spent $80 on a shirt. He paid the shirt using $20 and $10 bills. If she gave the clerk one more $20 bill than $10 bills, how many $10 bills did he give?
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