Update _filters/sum.md

Co-authored-by: Adam Klingbaum <[email protected]>

_filters/sum.md

@@ -7,7 +7,7 @@ Sums all items in an array.
 
 If a string is passed as an argument, it sums the property values.
 
-In this example, assume the object `collection.products` contains a list of products, and products has a `quantity` property. Using assign with the sum filter creates a variable that contains the total amount of quantities in all products from the collection.
+In this example, assume the object `collection.products` contains a list of products, and each `product` object has a `quantity` property. Using `assign` with the `sum` filter creates a variable that contains the total amount of quantities for all products in the collection.
 
 <p class="code-label">Input</p>
 ```liquid