Give the step-by-step reasoning process and then the final answer. 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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Andrea bought 45 / 3 = 15 rhinestones. She found 45 / 5 = 9 rhinestones in her supplies. Thus, Andrea still needs 45 - 15 - 9 = 21 rhinestones.
The final answer: 21.
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