docs: kata description

Author: ParanoidUser

kata/8-kyu/index.md

@@ -180,6 +180,7 @@
 - [Rock Paper Scissors!](rock-paper-scissors "5672a98bdbdd995fad00000f")
 - [Sentence Smash](sentence-smash "53dc23c68a0c93699800041d")
 - [Short Long Short](short-long-short "50654ddff44f800200000007")
+- [simple calculator ](simple-calculator "5810085c533d69f4980001cf")
 - [Simple Fun #1: Seats in Theater](simple-fun-number-1-seats-in-theater "588417e576933b0ec9000045")
 - [Simple multiplication](simple-multiplication "583710ccaa6717322c000105")
 - [Simple validation of a username with regex](simple-validation-of-a-username-with-regex "56a3f08aa9a6cc9b75000023")

kata/8-kyu/simple-calculator/README.md

@@ -0,0 +1,39 @@
+# [simple calculator ](https://www.codewars.com/kata/simple-calculator "https://www.codewars.com/kata/5810085c533d69f4980001cf")
+
+You are required to create a simple calculator that returns the result of addition, subtraction, multiplication or division of two numbers.
+
+Your function will accept three arguments:<br>
+The first and second argument should be numbers.<br>
+The third argument should represent a sign indicating the operation to perform on these two numbers.
+```if-not:csharp,java
+if the variables are not numbers or the sign does not belong to the list above a message "unknown value" must be returned.
+```
+```if:csharp,java
+If the sign is not a valid sign, throw an IllegalArgumentException (Java) or ArgumentException (C#).
+```
+
+# Example:
+
+~~~if-not:csharp,java
+```
+arguments: 1, 2, "+"
+should return 3
+
+arguments: 1, 2, "&"
+should return "unknown value"
+
+arguments: 1, "k", "*"
+should return "unknown value"
+```
+~~~
+~~~if:csharp,java
+```
+arguments: 1, 2, "+"
+should return 3
+
+arguments: 1, 2, "&"
+should throw an IllegalArgumentException (Java) or ArgumentException (C#)
+```
+~~~
+
+Good luck!