with someone else who's standing next to you, you're going to sum your numbers together and one of you whoever is fastest probably is going to sit down and the other person is going to take on his or her number, the summation of those numbers; and then you're going to repeat and if you follow the logic here in just a few moments, there should be just one of you very awkwardly standing.

你们需要与站在你下面一个的你结成一对,把你们的数字相加,你们中最快的那个可以坐下,其他人将接着他的那个号码继续进行，计算这些数字的和，以此重复,如果你们遵循了这一逻辑，最后将只有一个人呆呆地站着。

哈佛公开课 - 计算机科学课程节选

If you have a sample with n observations, it's the summation I = 1 to n of xi/n--that's the average.

如果你有n个观测值,对Xi从i=1到n求和再除以n

耶鲁公开课 - 金融市场课程节选

When we have n observations it's just the summation i = 1 to n of 2/n.

当有n个观察值,这就是在i取1到n时,x减去x均值的平方,除以n的累加

耶鲁公开课 - 金融市场课程节选