Andrea bought 45 / 3 = <<45/3=15>>15 rhinestones.

She found 45 / 5 = <<45/5=9>>9 rhinestones in her supplies.

Thus, Andrea still needs 45 - 15 - 9 = <<45-15-9=21>>21 rhinestones.

# Answer

21
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Andrea needs 45 rhinestones to finish an art project. She bought a third of what she needed and found a fifth of what she needed in her supplies. How many rhinestones does she still need?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
21
Andrea needs 45 rhinestones to finish an art project. She bought a third of what she needed and found a fifth of what she needed in her supplies. How many rhinestones does she still need?
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