If you buy 18 units, the percentage of the total price drops to 100% - 20% = 80%

If 80% is equal to $500, then 100% is equals 100%/80% * $500 = $625

# Answer

625
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
You can lower the price by 20% if you buy more than fifteen units of iPhone cases. If you pay $500 to buy 18 units, what is the original price?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
625
You can lower the price by 20% if you buy more than fifteen units of iPhone cases. If you pay $500 to buy 18 units, what is the original price?
train