minor typos in chapter 5 (#666)

transform.Rmd

@@ -101,7 +101,7 @@ There's another common problem you might encounter when using `==`: floating poi
 
 ```{r}
 sqrt(2) ^ 2 == 2
-1/49 * 49 == 1
+1 / 49 * 49 == 1
 ```
 
 Computers use finite precision arithmetic (they obviously can't store an infinite number of digits!) so remember that every number you see is an approximation. Instead of relying on `==`, use `near()`:
@@ -389,7 +389,7 @@ There are many functions for creating new variables that you can use with `mutat
 
 *   Offsets: `lead()` and `lag()` allow you to refer to leading or lagging 
     values. This allows you to compute running differences (e.g. `x - lag(x)`) 
-    or find when values change (`x != lag(x))`. They are most useful in 
+    or find when values change (`x != lag(x)`). They are most useful in 
     conjunction with `group_by()`, which you'll learn about shortly.
     
     ```{r}
@@ -882,7 +882,7 @@ Functions that work most naturally in grouped mutates and filters are known as
     
 1.  Delays are typically temporally correlated: even once the problem that
     caused the initial delay has been resolved, later flights are delayed 
-    to allow earlier flights to leave. Using `lag()` explore how the delay
+    to allow earlier flights to leave. Using `lag()`, explore how the delay
     of a flight is related to the delay of the immediately preceding flight.
     
 1.  Look at each destination. Can you find flights that are suspiciously