diff --git a/04- April/26- Add Digits/26- Add Digits (Noura Algohary).cpp b/04- April/26- Add Digits/26- Add Digits (Noura Algohary).cpp
new file mode 100644
index 000000000..b646fb405
--- /dev/null
+++ b/04- April/26- Add Digits/26- Add Digits (Noura Algohary).cpp	
@@ -0,0 +1,26 @@
+// Author: Noura Algohary
+// beats 100% in runtime 
+
+class Solution {
+public:
+    int recursiveAddition(string num)
+    {
+        // the ending contidion is reaching a one digit number
+        if(num.size() == 1)
+            return (num[0] - '0');
+
+        // to store the summation of digits of num
+        int sumInt = 0;
+
+        for(int i=num.size() - 1; i>=0; i--)
+        {
+            // convert the digit num[i] from char to int, then sum it
+            sumInt += num[i] - '0';
+        }
+        
+        return recursiveAddition(to_string(sumInt));
+    }
+    int addDigits(int num) {
+        return recursiveAddition(to_string(num));
+    }
+};
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diff --git a/04- April/26- Add Digits/26- Add Digits (Noura Algohary).py b/04- April/26- Add Digits/26- Add Digits (Noura Algohary).py
new file mode 100644
index 000000000..ed964d65b
--- /dev/null
+++ b/04- April/26- Add Digits/26- Add Digits (Noura Algohary).py	
@@ -0,0 +1,19 @@
+# Author: Noura Algohary
+
+class Solution:
+    def addDigits(self, num: int) -> int:
+
+        def recursiveAddition(num):
+            # the ending contidion is reaching a one digit number
+            if len(num) == 1:
+                return int(num)
+
+            # to store the summation of digits of num
+            sumInt = 0
+
+            for i in range(len(num) - 1, -1, -1):
+                sumInt += int(num[i])
+
+            return recursiveAddition(str(sumInt))
+
+        return recursiveAddition(str(num))
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diff --git a/04- April/26- Add Digits/26- Add Digits (RotenKiwi).cpp b/04- April/26- Add Digits/26- Add Digits (RotenKiwi).cpp
new file mode 100644
index 000000000..ebf0748cb
--- /dev/null
+++ b/04- April/26- Add Digits/26- Add Digits (RotenKiwi).cpp	
@@ -0,0 +1,13 @@
+// Author: RotenKiwi
+class Solution {
+public:
+    int addDigits(int num) {
+        if(num<10)return num;      // If  number is less than 10, retrn it.
+        int curr=0;               //  Variable to store the digit sum.
+        while(num){              // Calculation of digit sum.
+            curr=curr+(num%10);
+            num=num/10;
+        }
+        return addDigits(curr);       // Recurse the same for the new number
+    }
+};
diff --git a/04- April/26- Add Digits/26- Add Digits (Zeinab Mohy).cpp b/04- April/26- Add Digits/26- Add Digits (Zeinab Mohy).cpp
new file mode 100644
index 000000000..2f0f22c17
--- /dev/null
+++ b/04- April/26- Add Digits/26- Add Digits (Zeinab Mohy).cpp	
@@ -0,0 +1,31 @@
+// Author: Zeinab Mohy
+
+class Solution {
+public:
+    int addDigits(int num) {
+      //convert num into string to apply my idea
+        string s=to_string(num);
+      //if the length of string is greater than 1 then ..
+        if(s.length()>1){
+            while(s.length()>1){
+              /*initialize the summation of the digits with 0 
+              then sum the digits in string after convert all into integer 
+              then convert summatiomn into string again and so on 
+              until the length of string equal 1*/
+                int sum=0;
+                string ss;
+                for(int i=0;i<s.length();i++){
+                    ss=s[i];
+                    int x=stoi(ss);
+                    sum+=x;
+                }
+                s=to_string(sum);
+            }
+          // after that convert string into integer to return the result
+            int ans=stoi(s);
+            return ans;
+        }else{
+            return num;
+        }
+    }
+};
diff --git a/04- April/27- Bulb Switcher/27- Bulb Switcher (Mahmoud Aboelsoud).cpp b/04- April/27- Bulb Switcher/27- Bulb Switcher (Mahmoud Aboelsoud).cpp
new file mode 100644
index 000000000..9cf4470fd
--- /dev/null
+++ b/04- April/27- Bulb Switcher/27- Bulb Switcher (Mahmoud Aboelsoud).cpp	
@@ -0,0 +1,15 @@
+// Author: Mahmoud Aboelsoud
+
+class Solution {
+public:
+    int bulbSwitch(int n) {
+        // for this problem we need to know how many light bulbs are on after n rounds
+        // to know that you need to know for each light bulb to stay on at the end it needs to have odd number of divisors
+        // the only numbers that have odd number of divisors are perfect squares
+        // so the answer is the number of perfect squares less than or equal to n
+        // which is sqrt(n)
+
+
+        return sqrt(n);
+    }
+};
diff --git a/04- April/README.md b/04- April/README.md
index c38621b74..989d6e96d 100644
--- a/04- April/README.md	
+++ b/04- April/README.md	
@@ -49,6 +49,7 @@
 1. **[Last Stone Weight](#24--last-stone-weight)**
 1. **[Smallest Number in Infinite Set](#25--smallest-number-in-infinite-set)**
 1. **[Add Digits](#26--add-digits)**
+1. **[Bulb Switcher](#27--bulb-switcher)**
 
 <hr>
 <br><br>
@@ -1499,4 +1500,36 @@ public:
     }
 };
 ```
+    
+<hr>
+<br><br>
+
+## 27)  [Bulb Switcher](https://leetcode.com/problems/bulb-switcher/)
+
+### Difficulty
+
+![](https://img.shields.io/badge/Medium-orange?style=for-the-badge)
+
+### Related Topic
+
+`Math` `Brainteaser`
+
+### Code
+
+
+```cpp
+class Solution {
+public:
+    int bulbSwitch(int n) {
+        // for this problem we need to know how many light bulbs are on after n rounds
+        // to know that you need to know for each light bulb to stay on at the end it needs to have odd number of divisors
+        // the only numbers that have odd number of divisors are perfect squares
+        // so the answer is the number of perfect squares less than or equal to n
+        // which is sqrt(n)
+
+
+        return sqrt(n);
+    }
+};
+```
     
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