求助：一道题目怎么都读不懂 望朋友们指点

xlg24127

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 The list shown consists of the times,in seconds,that it took each of 10 schoolchildren to run a distance of 400 meters.If the standard deviation of the 10 running times is 22.4 seconds,rounded to 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?

先谢过朋友们了！

yunnan1990

把这十个数字相加，再除十，就是平均了。那么再从平均那里减去 standard deviation，看有多少数比差少。