x=round(runif(20,0,20),2)
x
mean(x)

结果：
> x=round(runif(20,0,20),2)
> x
[1]  5.15 12.63  7.39 17.26  5.29 12.99 18.18 10.50 12.93 12.56  9.65  6.74
[13] 13.55  4.02 15.95  7.47 19.73 12.59  0.83  1.54
> mean(x)
[1] 10.3475
？？？