Update Functions.Rmd (#526)

I think there is a typo in wt_mean because if it's a weighted mean of x with weights w it should be sum(x * w) / sum(w)

functions.Rmd

@@ -528,7 +528,7 @@ As you start to write more functions, you'll eventually get to the point where y
 
 ```{r}
 wt_mean <- function(x, w) {
-  sum(x * w) / sum(x)
+  sum(x * w) / sum(w)
 }
 wt_var <- function(x, w) {
   mu <- wt_mean(x, w)
@@ -554,7 +554,7 @@ wt_mean <- function(x, w) {
   if (length(x) != length(w)) {
     stop("`x` and `w` must be the same length", call. = FALSE)
   }
-  sum(w * x) / sum(x)
+  sum(w * x) / sum(w)
 }
 ```
 
@@ -577,7 +577,7 @@ wt_mean <- function(x, w, na.rm = FALSE) {
     x <- x[!miss]
     w <- w[!miss]
   }
-  sum(w * x) / sum(x)
+  sum(w * x) / sum(w)
 }
 ```
 
@@ -593,7 +593,7 @@ wt_mean <- function(x, w, na.rm = FALSE) {
     x <- x[!miss]
     w <- w[!miss]
   }
-  sum(w * x) / sum(x)
+  sum(w * x) / sum(w)
 }
 wt_mean(1:6, 6:1, na.rm = "foo")
 ```