diff --git a/factors.Rmd b/factors.Rmd
index 537f69d..f00b959 100644
--- a/factors.Rmd
+++ b/factors.Rmd
@@ -64,7 +64,7 @@ y2 <- factor(x2, levels = month_levels)
 y2
 ```
 
-If you want a want, you can use `readr::parse_factor()`:
+If you want an error, you can use `readr::parse_factor()`:
 
 ```{r}
 y2 <- parse_factor(x2, levels = month_levels)
diff --git a/transform.Rmd b/transform.Rmd
index 30fac27..ccae33c 100644
--- a/transform.Rmd
+++ b/transform.Rmd
@@ -773,7 +773,7 @@ Just using means, counts, and sum can get you a long way, but R provides many ot
     # What proportion of flights are delayed by more than an hour?
     not_cancelled %>% 
       group_by(year, month, day) %>% 
-      summarise(hour_perc = mean(arr_delay > 60, na.rm = TRUE))
+      summarise(hour_perc = mean(arr_delay > 60))
     ```
 
 ### Grouping by multiple variables