GMAT
题目
Two musicians, Maria and Perry, work at independent constant rates to tune a warehouse full of instruments. If both musicians start at the same time and work at their normal rates, they will complete the job in 45 minutes. However, if Perry were to work at twice Maria’s rate, they would take only 20 minutes. How long would it take Perry, working alone at his normal rate, to tune the warehouse full of instruments?
解析
公式：速率×时间 = 工作量
两人合作时：
\( (P + M) × \frac{3}{4} = 1 \)
已知\( P = 2M \)，代入得：
\( (2M + M) × \frac{1}{3} = 1 \)，由此解得\( M = 1 \)
将\( M = 1 \)代入最初的方程：
\( \frac{3}{4}P + \frac{3}{4} = 1 \)，即\( \frac{3}{4}P = \frac{1}{4} \)，解得\( P = \frac{1}{3} \)
因此，P单独完成这项工作需要3小时（因为\( \frac{1}{3} × 3h = 1 \)份工作）
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