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精英家教網 > 初中數學 > 題目詳情
There is a piece of work．It takes Mr．A alone 20 days to finish，and Mr．B 30 alone days to finish．It takes them（　　）days to work together to finish the work．
A、10B、12C、15D、50
分析：設他們一起工作x天可結束工作，根據工作量=工作時間×工作效率，完成工作工作量為1，根據題意可列方程求解．
解答：解：設他們一起工作x天可結束工作．
（
1
20
+
1
30
）x=1
x=12
需要12天可完成工作．
故選B．
點評：本題考查理解題意能力，關鍵是知道工作量=工作時間×工作效率，完成工作工作量為1，從而列方程可得解．
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