snippet.js

// Math.sum.apply(null, [3, 4, 5, 6]) => 18
Math.sum = function() {
	var total = 0, x = 0;
	while (x < arguments.length) total += arguments[x++];
	return total;
};

// Math.avg.apply(null, [3, 4, 5, 6]) => 4.5
Math.avg = function() {
	return Math.sum.apply(null, arguments) / arguments.length;
};