const marks = [80, 90, 70, 60];
let averageMarks = marks.reduce((total, eachMark)=>{
total += eachMark;
return total
}, 0);
console.log(averageMarks / marks.length);
//output : 75
/* in one line */
let avg = marks.reduce((sum, eachmarks)=> sum + eachmarks, 0);
console.log(avg / marks.length);
// output : 75 
