index.js

var questions = [
  "Two + Three",
  "Five + Four",
  "Nine - Two",
  "Five - Three",
  "Six + Three"
];
var answers = [
  5, 9, 7, 2, 9
];
var numbers = [
  "Zero",
  "One",
  "Two",
  "Three",
  "Four",
  "Five",
  "Six",
  "Seven",
  "Eight",
  "Nine"
];

// Solution if you're bored
var randIndexA = Math.floor(Math.random() * numbers.length); // Number #1
var randIndexB = Math.floor(Math.random() * numbers.length); // Number #2
var a = Math.round(Math.random() * 1); // 0 for minus, 1 for plus
var b;
if ( a ) { b = " + "; } else { b = " - "; }

console.log( "First number is: " + randIndexA + " (" + numbers[randIndexA] + ")" );
console.log( "First number is: " + randIndexB + " (" + numbers[randIndexB] + ")" );
console.log( "Math symbol to use:" + b );

$("#question").html( numbers[randIndexA] + b + numbers[randIndexB] );

$("#checkAnswer").click(function() {

  console.log("Check Answer was clicked!");

  var userIn = parseInt( $( "#userinput" ).val() );
  var message = ( calculate(randIndexA, randIndexB, a) === userIn )
                  ? "You're a human"
                  : "You're either a robot or bad at math"
  ;

  $( "#result" ).html(message);
});

// Add or subtract two numbers based on a custom operator.
function calculate(a, b, sign) {
  if (sign === 1) { // I just like to be ultra clear here.
    return (a + b);
  } else {
    return (a - b);
  }
}