Minor fixes and small notes

logicals-numbers.Rmd

@@ -333,11 +333,14 @@ near(1 / 49 * 49, 1)
 
 Alternatively, you might want to use `round()` to trim off extra digits.
 
-## Exercises
+### Exercises
 
-1.  What trigonometric functions does R provide?
+1.  Currently `dep_time` and `sched_dep_time` are convenient to look at, but hard to compute with because they're not really continuous numbers.
+    Convert them to a more convenient representation of number of minutes since midnight.
 
-2.  Brainstorm at least 5 different ways to assess the typical delay characteristics of a group of flights.
+2.  What trigonometric functions does R provide?
+
+3.  Brainstorm at least 5 different ways to assess the typical delay characteristics of a group of flights.
     Consider the following scenarios:
 
     -   A flight is 15 minutes early 50% of the time, and 15 minutes late 50% of the time.

missing-values.Rmd

@@ -151,6 +151,8 @@ treatment %>%
   fill(person)
 ```
 
+`group_by` + `.drop = FALSE`
+
 ### Exercises
 
 1.  Compare and contrast the `fill` arguments to `pivot_wider()` and `complete()`.

workflow-pipes.Rmd

@@ -116,4 +116,3 @@ But they're good to know about even if you've never used `%>%`, because you're l
 
 -   Starting a pipe with `.`, like `. %>% group_by(x) %>% summarise(x)` would create a function rather than immediately performing the pipe.
     This is an error with the base pipe.
-