The difference between the initial cost and the amount she sold the phone for is $300-$255 = $<<300-255=45>>45 $45 is (($45/$300)*100)% = 15% of $300

# Answer

15
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Matilda bought a smartphone for $300. Then she decided she wouldn't use it anyway and sold it for $255. What percentage of the initial cost did she lose?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
15
Matilda bought a smartphone for $300. Then she decided she wouldn't use it anyway and sold it for $255. What percentage of the initial cost did she lose?
train