帮帮我吧数学题谢谢谢！！

guo573874201 · 发表于 2011-9-15 02:02:24

2. In the decimal representation of x, where 0 < x < 1, is the tenths digit if x nonzero?
(1)16x is an integer.
(2)8x is an integer.答案选B 为什么第一个条件不可以呢

3. Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long.Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure.The two trains passed each other after traveling for 2 hours.When the two trains passed, which train was nearer to its destination?
(1)At the time when the two trains passed, train P had averaged a speed of 70 miles per hour.
(2)Train Q averaged a speed of 55 miles per hour for the entire trip. 答案选A 条件1.2 都可以求出来呀

帮帮我吧具体思路和过程

nelly000 · 发表于 2011-9-15 02:25:26

1 设总税前消费S 消费税=S*50%*4%+S*30%*8%=4.4%S
ratio=4.4%

2 条件1不充分的原因是1/16=0.0625 2/16=0.125 所以十分位可能为0可能为非零
条件2充分 1/8=0.125 如果整数更大，十分位都是非零的。。。。。

3条件1充分是因为强调了相遇时的平均速度 2没有提到相遇而是全程，如果Q不匀速，没法算出相遇时行驶的距离。。。。

帮帮我吧数学题谢谢谢！！

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