JS Bin// source http://jsbin.com/kixipiqeka

jsbin.kixipiqeka.js

const numbers = [10, 20, 30, 40];

let updatedNumbers = numbers
                      .map((num) => num * 2)
                      .filter((num) => num > 50);

let doubledOver50 = numbers.reduce((finalList, num) => {
  num = num * 2; //double each number (i.e. map)
  //filter number > 50
  if (num > 50) {
    finalList.push(num);
  }
  return finalList;
}, []);

console.log(updatedNumbers)
console.log(doubledOver50)