diff --git a/iteration.Rmd b/iteration.Rmd
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--- a/iteration.Rmd
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@@ -158,7 +158,7 @@ That's all there is to the for loop! Now is a good time to practice creating som
 
 ## For loop variations
 
-Once you have the basic for loop under your belt, there are some variations that you should be aware of. These variations are important regardless of how you do iteration, so don't forget about them once you've master the FP techniques you'll learn about in the next section.
+Once you have the basic for loop under your belt, there are some variations that you should be aware of. These variations are important regardless of how you do iteration, so don't forget about them once you've mastered the FP techniques you'll learn about in the next section.
 
 There are four variations on the basic theme of the for loop: