On monday Rhonda made an average of 12 phone calls per hour for the first 6 calls she made , and then an average of 6 phone calls per hour for the remaining 6 calls she made

题目

On monday Rhonda made an average of 12 phone calls per hour for the first 6 calls she made , and then an average of 6 phone calls per hour for the remaining 6 calls she made. What was the average number of phone calls per hour that Rhonda made for the entire day

选项

7.5

8.0

9.5

10.0

10.5

解析

这里有两组各6通电话，是在两种不同频率下拨打的。我们来计算这些电话的耗时：（i）以每小时12通的速率拨打6通电话如果1小时能打12通，那么6通电话需要的时间是\( 6 × \frac{1}{12} = \frac{1}{2} \)小时（ii）以每小时6通的速率拨打6通电话这部分电话需要1小时因此，总通话数=6+6=12通，总耗时=\( 1 + \frac{1}{2} = \frac{3}{2} \)小时每小时平均通话数=\( \frac{\text{通话数}}{\text{时间}} = 12 ÷ \frac{3}{2} = \frac{12×2}{3} = 8 \)通/小时答案：B

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