diff --git a/Exercises/1-hoisting.js b/Exercises/1-hoisting.js
index 0920026..7a69046 100644
--- a/Exercises/1-hoisting.js
+++ b/Exercises/1-hoisting.js
@@ -1,5 +1,7 @@
 'use strict';
 
-const fn = null;
+const fn = () => {
+  const a = 5;
+};
 
 module.exports = { fn };
diff --git a/Exercises/2-by-value.js b/Exercises/2-by-value.js
index f576b24..e7652d5 100644
--- a/Exercises/2-by-value.js
+++ b/Exercises/2-by-value.js
@@ -1,5 +1,5 @@
 'use strict';
 
-const inc = null;
+const inc = a => ++a;
 
 module.exports = { inc };
diff --git a/Exercises/3-by-reference.js b/Exercises/3-by-reference.js
index f576b24..be65287 100644
--- a/Exercises/3-by-reference.js
+++ b/Exercises/3-by-reference.js
@@ -1,5 +1,9 @@
 'use strict';
 
-const inc = null;
+const inc = num => {
+  if (typeof num === 'object') {
+    ++num.n;
+  }
+};
 
 module.exports = { inc };
diff --git a/Exercises/4-count-types.js b/Exercises/4-count-types.js
index 4c9545a..b67b373 100644
--- a/Exercises/4-count-types.js
+++ b/Exercises/4-count-types.js
@@ -1,5 +1,13 @@
 'use strict';
 
-const countTypesInArray = null;
+const countTypesInArray = array => {
+  const obj = {};
+  array.forEach(item => {
+    const type = typeof item;
+    const count = obj[type] || 0;
+    obj[type] = count + 1;
+  });
+  return obj;
+};
 
 module.exports = { countTypesInArray };
diff --git a/package-lock.json b/package-lock.json
index 33eaeb2..f235cea 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -576,7 +576,7 @@
       "resolved": "https://registry.npmjs.org/mkdirp/-/mkdirp-0.5.1.tgz",
       "integrity": "sha1-MAV0OOrGz3+MR2fzhkjWaX11yQM=",
       "requires": {
-        "minimist": "1.2.5"
+        "minimist": "0.0.8"
       },
       "dependencies": {
         "minimist": {