x = 10/runif(10^5)^.5
pm = sample(c(-1,1),10^5, rep=T)
y = x*pm
hist(y[abs(y) < 100], prob=T, br=50)

x1 = rexp(10^5, 1);  x2 = rexp(10^5, 1)
y = x1 - x2
mean(y);  var(y)
[1] 0.006819823
[1] 1.989892
hist(y, prob=T, br=50, col="skyblue2")