Why does the the first way work but not the second?

Question

function main() {
var num1 = parseInt(readLine(),10);
var num2 = parseInt(readLine(),10);
var num3 = parseInt(readLine(),10);

var average = (avg(num1,num2,num3 ) / 3)

console.log(average)

function avg(n1,n2,n3){ return n1 + n2 + n3

}

Vs

function main() {
var num1 = parseInt(readLine(),10);
var num2 = parseInt(readLine(),10);
var num3 = parseInt(readLine(),10);

var average = (avg(num1,num2,num3 ))

console.log(average)

}

function avg(n1,n2,n3){ return n1 + n2 + n3 / 3

}

Answer 1

In 2nd way, you have to use return (n1+n2+n3)/3

Answer 2

2nd doesn't works because:

n1+n2+n3/3 == n1+n2+(n3/3) != (n1+n2+n3)/3