2. 外语
  3. The charge for a telephone call made at 10: 00 a. m. from City Y to City X is $ 0. 50 for the first minute and $ 0. 34 for each

The charge for a telephone call made at 10: 00 a. m. from City Y to City X is $ 0. 50 for the first minute and $ 0. 34 for each

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问题 The charge for a telephone call made at 10: 00 a. m. from City Y to City X is $ 0. 50 for the first minute and $ 0. 34 for each additional minute. At these rates, what is the difference between the total cost of three 5-minute calls and the cost of one 15-minute call?
选项 A、$0
B、$0.16
C、$0.32
D、$0.48
E、$1
答案C
解析 上午10点时从Y城向X城打电话，第一分钟收费0.5美元，此后每附加一分钟收0.34美元。以这个标准计费，打3个5分钟的电话与打一个15分钟的电话之间的差价是多少?
解：本题的正确答案是(C)。3个5分钟的电话费为：3×(0.5+0.34×4)=5.58；15分钟的电话费：0.5+0.34×14=5.26；差价为：5.58-5.26=0.32。本题还有一个较为简便的算法，3个5分钟的电话与一个15分钟的电话的时间相同，它们惟一的区别是3个5分钟的电话比一个15分钟的电话多了两个“第一分钟"，考生只要找出这两个“第一分钟”与两个“非第一分钟”的差价就可以了，即为2×(0.5-0.34)=0.32。
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