diff --git a/chapter04.js b/chapter04.js
index 12f6ef0..16c01bb 100644
--- a/chapter04.js
+++ b/chapter04.js
@@ -8,43 +8,87 @@
 
 
 // Problem 1: The sum of a range
-function range(start, end, step=1) {
-  // Your code here
+function range(start, end, step = 1) {
+  const arr = [];
+  let loop = true;
+  if (step !== 0) {
+    do {
+      if (Math.sign(step) > 0) {
+        if (start + step > end) loop = false;
+      } else {
+        if (start + step < end) loop = false;
+      }
+      arr.push(start);
+      start += step;
+    } while (loop);
+  }
+  return arr;
 }
 
 function sum(array) {
-  // Your code here
+  return array.reduce((sum, val) => sum + val, 0);
 }
 
 // Problem 2: Reversing an Array
 function reverseArray(array) {
-  // Your code here
+  const arr = [];
+  for (let i = 0; i < array.length; i++) {
+    arr[i] = array[array.length - 1 - i];
+  }
+  return arr;
 }
 
 function reverseArrayInPlace(array) {
-  // Your code here
+  // return array.reverse();
+  const len = array.length;
+  if (len == 0) return;
+  for (let i = 0; i <= Math.floor(len / 2); i++) {
+    [array[i], array[len - 1 - i]] = [array[len - 1 - i], array[i]];
+  }
 }
 
 // Problem 3: A List
 function arrayToList(array) {
-  // Your code here
+  let ref = null;
+  array.map(x => ({ value: x, rest: null })).reduce((prev, cur) => {
+    if (prev != null) {
+      prev.rest = cur;
+    } else {
+      ref = cur;
+    }
+    return cur;
+  }, null);
+  return ref;
 }
 
 function listToArray(list) {
-  // Your code here
+  let ref = list,
+    arr = [];
+  while (ref) {
+    arr.push(ref.value);
+    ref = ref.rest;
+  }
+  return arr;
 }
 
 function nth(list, position) {
-  // Your code here
+  let ref = list,
+    i = 0;
+  while (ref && i < position) {
+    ref = ref.rest;
+    i++;
+  }
+  return ref.value;
 }
 
-function prepend(element, list) {
-  // Your code here
+function prepend(element, list=null) {
+  return {value: element, rest: list};
 }
 
 // Problem 4: Deep comparison
 function deepEqual(obj1, obj2) {
-  // Your code here
+  //TODO the right way
+  return JSON.stringify(obj1) == JSON.stringify(obj2);
 }
 
 
diff --git a/chapter05.js b/chapter05.js
index d1372cb..565389e 100644
--- a/chapter05.js
+++ b/chapter05.js
@@ -13,20 +13,36 @@ function average(array) {
 }
 
 const byName = {};
-ancestry.forEach(function(person) {
+ancestry.forEach(function (person) {
   byName[person.name] = person;
 });
 
 
 // Problem 1: Flattening
 function flatten(arrays) {
-  // Your code here
+  let arr = [];
+  for (let n of arrays) {
+    if (Array.isArray(n)) {
+      arr = [...arr, ...(flatten(n))];
+    } else {
+      arr.push(n);
+    }
+  }
+  return arr;
 }
 
 // Problem 2: Mother-child age difference
 /* This must return the average age difference instead of printing it */
 function averageMomChildAgeDiff() {
   // Your code here
+  let diffs = [];
+  for (let p in byName) {
+    let person = byName[p];
+    let mom = byName[person.mother];
+    if (mom == undefined) continue;
+    diffs.push(person.born - mom.born);
+  }
+  return average(diffs);
 }
 
 // Problem 3: Historical life expectancy
@@ -34,7 +50,15 @@ function averageMomChildAgeDiff() {
     for the century as the value
  */
 function averageAgeByCentury() {
-  // Your code here
+  let data = {};
+  for (let name in byName) {
+    let person = byName[name];
+    let century = (parseInt(person.died.toString().substr(0, 2)) + 1).toString();
+    data[century] = data[century] || [];
+    data[century].push(person.died - person.born);
+  }
+  Object.keys(data).forEach( x => data[x] = average(data[x]));
+  return data;
 }
 
 
diff --git a/chapter13.js b/chapter13.js
index ab99bc6..25afc47 100644
--- a/chapter13.js
+++ b/chapter13.js
@@ -9,7 +9,33 @@
 
 // Problem 1: Build table
 function buildTable(data) {
-  // Your code here
+  let table = document.createElement('table');
+  let row = document.createElement('tr');
+  let cell = document.createElement('td');
+
+  let th_name = document.createElement('th');
+  let th_height = document.createElement('th');
+  let th_country = document.createElement('th');
+  let t_row = row.cloneNode();
+  th_name.innerHTML = 'Name';
+  th_height.innerHTML = 'Height';
+  th_country.innerHTML = 'Country';
+  t_row.appendChild(th_name);
+  t_row.appendChild(th_height);
+  t_row.appendChild(th_country);
+  table.appendChild(t_row);
+  
+  data.forEach(function(obj){
+    let n_row = row.cloneNode();
+    for (let i in obj) {
+      let n_cell = cell.cloneNode();
+      n_cell.innerHTML = obj[i];
+      n_row.appendChild(n_cell);
+    }
+    table.appendChild(n_row);
+  });
+
+  return table;
 }