1950 AMC 12 第 29 题
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所有题目均经美国数学协会（MAA）官方合法授权使用。
29.
某制造商造了一台机器，可在 分钟内给 个信封书写地址。他希望再造一台机器，使两台机器同时工作时能在 分钟内完成 个信封。若第二台机器单独完成 个信封需要 分钟，则求该时间所用的方程为：
A manufacturer built a machine which will address envelopes in minutes. He wishes to build another machine so that when both are operating together they will address envelopes in minutes. The equation used to find how many minutes it would require the second machine to address envelopes alone is:
以上答案均不正确
None of these answers
小提示：
以每分钟完成多少批 个信封来表示各台机器的效率
Measure each machine’s rate in batches of envelopes per minute
大提示：
两台机器各自的效率之和等于共同工作的效率
The two individual rates must add to the combined rate
解答：
第一台机器每分钟完成一批 个信封的 ，第二台每分钟完成一批的 。两台一起工作时，每分钟必须完成一批的 。因此，所需方程为
因此，正确答案是 B。
The first machine completes of a -envelope batch per minute, and the second completes of a batch per minute. Together they must complete of a batch per minute. Therefore the required equation is
Thus, the correct answer is B.
其他年份的第 29 题
- 1951 AMC 12
- 1952 AMC 12
- 1953 AMC 12
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- 1955 AMC 12
- 1956 AMC 12
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