Sum numbers returns NaN

Answer 1

Try this

var numbers=0, sumNumbers=0; //initilize numbers & sumNumbers;

$(".item").each(function () {
    numbers = $(this).children().text() * 1; // *1 convert string to number

    sumNumbers += numbers;
});

console.log(sumNumbers);

Answer 2

You didn't initialize sumNumbers, so you get undefined + a number = NaN

var numbers, sumNumbers = 0;