diff --git a/modules/3_objects/index.js b/modules/3_objects/index.js
index b1985b8..60091a0 100644
--- a/modules/3_objects/index.js
+++ b/modules/3_objects/index.js
@@ -1,23 +1,55 @@
 /**
  * Array to List
  */
-export const arrayToList = () => {};
-export const listToArray = () => {};
+export const arrayToList = (arr) => {
+    let parentNode = {};
+    let childNode = parentNode;
+    for (let i = 0; i < arr.length; i++) {
+      childNode.value = arr[i];
+        if (i+1 !== arr.length){   
+          childNode.rest = {}
+          childNode = childNode.rest;
+        }else {
+          childNode.rest = null;
+        }
+        
+    }
+    return parentNode;
+};
+export const listToArray = (arr) => {
+    return arr; // not clear what should be done here
+};
 
 /**
  * Keys and values to list
  */
-export const getKeyValuePairs = () => {};
+export const getKeyValuePairs = (obj) => {
+    let result = [];
+    for (const key in obj) {
+        result.push([key, obj[key]]);
+    }
+    return result;
+};
 
 /**
  * Invert keys and values
  */
-export const invertKeyValue = () => {};
+export const invertKeyValue = (obj) => {
+    let result = {};
+    for (const key in obj) {
+        result[obj[key]] = key;
+    }
+    return result;
+};
 
 /**
  * Get all methods from object
  */
-export const getAllMethodsFromObject = () => {};
+export const getAllMethodsFromObject = (obj) => {
+    return Object.getOwnPropertyNames(obj).filter(function(property) {
+        return typeof obj[property] == 'function';
+    });
+};
 
 /**
  * Clock
@@ -27,4 +59,29 @@ export class Clock {}
 /**
  * Groups
  */
-export class Groups {}
+export class Groups {
+    members = [];
+
+    has(val){
+        return this.members.includes(val);
+    }
+
+    add(val){
+        if(!this.has(val)){
+            this.members.push(val);
+        }
+    }
+
+    delete(val){
+        if(this.has(val)){
+            let idx = this.members.indexOf(val);
+            this.members.splice(idx, 1);
+        }
+    }
+
+    static from (arr) {
+        let instance = new Groups();
+        instance.members = arr;
+        return instance;
+    }
+}