Phrase: The number of people increased by thirteen.
Variable: Let represents the number of people.
Expressions: .
Therefore, the algebraic expression is .
The algebraic expression is .
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represents the number of people.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=1474ef608f810dd2e0001e07ed3bab06.png\")
.![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=1474ef608f810dd2e0001e07ed3bab06.png\")
.![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")
.