[求助]这倒数学题怎么做啊

looklove

70 ，75， 80 ，85 ，90 ，105 ，105 ，130 ，130 ,130

The list shown consists of the times, in secound, that it took esch of 10 schoolchildren to run a distance of 400 meters. If the standard deviation of the running times is 22.4 secounds, rounded ti the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times?

[此贴子已经被作者于2008-1-12 14:13:41编辑过]

cyyp

9个数亚，怎么会是10个人？

方法应该是先求平均数，然后用平均数减掉22.4求得一个值，要考虑题目中的四舍五入到小数点后第一位。

最后看那些时间小于这个值，这就是最后结果。