diff --git a/Exercises/1-for.js b/Exercises/1-for.js
index 62e6ab8..1e10361 100644
--- a/Exercises/1-for.js
+++ b/Exercises/1-for.js
@@ -1,9 +1,13 @@
 'use strict';
 
 const sum = (...args) => {
-  // Use for loop and accumulator variable
-  // to calculate sum of all given arguments
-  // For example sum(1, 2, 3) should return 6
+  let answer = 0;
+
+  for (let i = 0; i < args.length; ++i) {
+    answer += args[i];
+  }
+
+  return answer;
 };
 
 module.exports = { sum };
diff --git a/Exercises/2-for-of.js b/Exercises/2-for-of.js
index 9965f25..b324211 100644
--- a/Exercises/2-for-of.js
+++ b/Exercises/2-for-of.js
@@ -1,9 +1,13 @@
 'use strict';
 
 const sum = (...args) => {
-  // Use for..of loop and accumulator variable
-  // to calculate sum of all given arguments
-  // For example sum(1, 2, 3) should return 6
+  let answer = 0;
+
+  for (const num of args) {
+    answer += num;
+  }
+
+  return answer;
 };
 
 module.exports = { sum };
diff --git a/Exercises/3-while.js b/Exercises/3-while.js
index 6110b9f..48f1b2f 100644
--- a/Exercises/3-while.js
+++ b/Exercises/3-while.js
@@ -1,9 +1,13 @@
 'use strict';
 
 const sum = (...args) => {
-  // Use while loop and accumulator variable
-  // to calculate sum of all given arguments
-  // For example sum(1, 2, 3) should return 6
+  let answer = 0;
+
+  while (args.length > 0) {
+    answer += args.pop();
+  }
+
+  return answer;
 };
 
 module.exports = { sum };
diff --git a/Exercises/4-do-while.js b/Exercises/4-do-while.js
index 22d4464..6fc2674 100644
--- a/Exercises/4-do-while.js
+++ b/Exercises/4-do-while.js
@@ -1,9 +1,15 @@
 'use strict';
 
 const sum = (...args) => {
-  // Use do..while loop and accumulator variable
-  // to calculate sum of all given arguments
-  // For example sum(1, 2, 3) should return 6
+  let answer = 0;
+
+  if (args.length === 0) return answer;
+
+  do {
+    answer += args.pop();
+  } while (args.length > 0);
+
+  return answer;
 };
 
 module.exports = { sum };
diff --git a/Exercises/5-reduce.js b/Exercises/5-reduce.js
index a9cb44c..9840bca 100644
--- a/Exercises/5-reduce.js
+++ b/Exercises/5-reduce.js
@@ -1,8 +1,5 @@
 'use strict';
 
-const sum = (...args) => 0;
-// Use Array.prototype.reduce method
-// to calculate sum of all given arguments
-// For example sum(1, 2, 3) should return 6
+const sum = (...args) => args.reduce((a, b) => a + b, 0);
 
 module.exports = { sum };
diff --git a/Exercises/6-matrix.js b/Exercises/6-matrix.js
index 0bc42c8..80c4ec5 100644
--- a/Exercises/6-matrix.js
+++ b/Exercises/6-matrix.js
@@ -1,9 +1,16 @@
 'use strict';
 
 const max = (matrix) => {
-  // Use nested for loop to find max value in 2d matrix
-  // For example max([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
-  // should return 9
+  let maxNum = 0;
+
+  for (let i = 0; i < matrix.length; ++i) {
+    for (let j = 0; j < matrix[i].length; ++j) {
+      const num = matrix[i][j];
+      maxNum =  num > maxNum ? num : maxNum;
+    }
+  }
+
+  return maxNum;
 };
 
 module.exports = { max };
diff --git a/Exercises/7-ages.js b/Exercises/7-ages.js
index e90caa2..e7f4e0b 100644
--- a/Exercises/7-ages.js
+++ b/Exercises/7-ages.js
@@ -1,19 +1,14 @@
 'use strict';
 
 const ages = (persons) => {
-  // Use for..in to calculate age for each person
-  // For example ages({
-  //   lenin: { born: 1870, died: 1924 },
-  //   mao: { born: 1893, died: 1976 },
-  //   gandhi: { born: 1869, died: 1948 },
-  //   hirohito: { born: 1901, died: 1989 },
-  // })
-  // should return {
-  //   lenin: 54,
-  //   mao: 83,
-  //   gandhi: 79,
-  //   hirohito: 88,
-  // }
+  const arrYears = {};
+
+  for (const people in persons) {
+    const age = persons[people].died - persons[people].born;
+    arrYears[people] = age;
+  }
+
+  return arrYears;
 };
 
 module.exports = { ages };