You meet a man on the street and he says, “I have two children and one is a son born on a Tuesday.” What is the probability that the other child is also a son?

test.js

function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

function getRandomChild() {
  return {
    gender: getRandomInt(0, 1),
    dayOfBirth: getRandomInt(0, 6)
  }
}

function getSpecialChild() {
  return {
    gender: 0,
    dayOfBirth: 1
  }
}

function isMale(child) {
  return child.gender === 0;
}

function isBornTuesday(child) {
  return child.dayOfBirth === 1;
}

// Check if a pair of kids is both male.
function isTwoBoys(pair) {
  var c1 = pair[0];
  var c2 = pair[1];
  return isMale(c1) && isMale(c2);
}

// Check in a given pair of kids, one of them is a male born on tuesday
// and the other is a boy, born on any day.
function isTwoBoysOneBornTuesday(pair) {
  var c1 = pair[0];
  var c2 = pair[1];
  
  var cond1 = isMale(c1) && isBornTuesday(c1) && isMale(c2);
  var cond2 = isMale(c2) && isBornTuesday(c2) && isMale(c1);

  return cond1 || cond2;
}

// Check in a given pair of kids, one of them is a male born on tuesday
// and the other is a boy but not born on a tuesday.
function isTwoBoysOnlyOneBornTuesday(pair) {
  var c1 = pair[0];
  var c2 = pair[1];
  
  var cond1 = isMale(c1) && !isBornTuesday(c1) && isBornTuesday(c2) && isMale(c2);
  var cond2 = isMale(c2) && !isBornTuesday(c2) && isBornTuesday(c1) && isMale(c1);

  return cond1 || cond2;
}


// Run!
var iteration = 1000000;
var population = []

// Don't really need this but makes it easier to see population.
for (var i = 0; i < iteration; i++) {
  population.push([getRandomChild(), getSpecialChild()])
}

var q1 = q2 = q3 = 0;
for (var i=0; i < population.length; i++) {
  var pair = population[i];
  if (isTwoBoys(pair)) {
    q1++;
  }
  if (isTwoBoysOneBornTuesday(pair)) {
    q2++;
  }
  if (isTwoBoysOnlyOneBornTuesday(pair)) {
    q3++;
  }
}

console.log('\nIteration:', iteration);
console.log('\nQuestion 1: Two boys\n', q1/iteration);
console.log('\nQuestion 2: Two boys, one born on Tuesday\n', q2/iteration);
console.log('\nQuestion 2: Two boys, only one born on Tuesday\n', q3/iteration);
console.log('\n-- REFERENCE --')
console.log('1  / 2:\t\t', 1/2);
console.log('13 / 27:\t', 13/27);
console.log('12 / 28:\t', 12/28);