diff --git a/Exercises/1-hoisting.js b/Exercises/1-hoisting.js
index 0920026..ab6ab6b 100644
--- a/Exercises/1-hoisting.js
+++ b/Exercises/1-hoisting.js
@@ -1,5 +1,8 @@
 'use strict';
 
-const fn = null;
+const fn = function raising() {
+  const variable = 'Hello';
+  console.log(variable);
+};
 
 module.exports = { fn };
diff --git a/Exercises/2-by-value.js b/Exercises/2-by-value.js
index f576b24..80e623e 100644
--- a/Exercises/2-by-value.js
+++ b/Exercises/2-by-value.js
@@ -1,5 +1,9 @@
 'use strict';
 
-const inc = null;
+const inc = (x) => ++x;
+
+// function inc(n) {
+//   return n+1;
+// }
 
 module.exports = { inc };
diff --git a/Exercises/3-by-reference.js b/Exercises/3-by-reference.js
index 74638ec..c7e21a3 100644
--- a/Exercises/3-by-reference.js
+++ b/Exercises/3-by-reference.js
@@ -1,7 +1,15 @@
 'use strict';
 
-const inc = (obj) => {
-  console.log(obj);
+const inc = function(obj) {
+  obj.n += 1;
 };
 
+// function inc(num) {
+//   if (num && typeof num.n === 'number') {
+//     num.n += 1;
+//   } else {
+//     throw new Error("Invalid input: Object must have a numeric 'n' field");
+//   }
+// }
+
 module.exports = { inc };
diff --git a/Exercises/4-count-types.js b/Exercises/4-count-types.js
index 4c9545a..ff1faae 100644
--- a/Exercises/4-count-types.js
+++ b/Exercises/4-count-types.js
@@ -1,5 +1,12 @@
 'use strict';
 
-const countTypesInArray = null;
+function countTypesInArray(arr) {
+  const result = {};
+  for (const item of arr) {
+    const type = typeof item;
+    result[type] = (result[type] || 0) + 1;
+  }
+  return result;
+}
 
 module.exports = { countTypesInArray };