Fix typo (#5111)

Author: thomcleary

beta/src/content/learn/updating-arrays-in-state.md

@@ -214,7 +214,7 @@ Here, `artists.filter(a => a.id !== artist.id)` means "create an array that cons
 
 If you want to change some or all items of the array, you can use `map()` to create a **new** array. The function you will pass to `map` can decide what to do with each item, based on its data or its index (or both).
 
-In this example, an array holds coordinates of two circles and a square. When you press the button, it moves only the circles down by 100 pixels. It does this by producing a new array of data using `map()`:
+In this example, an array holds coordinates of two circles and a square. When you press the button, it moves only the circles down by 50 pixels. It does this by producing a new array of data using `map()`:
 
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