diff --git a/isbn-verifier/src/lib.rs b/isbn-verifier/src/lib.rs
index f2f9502..0672051 100644
--- a/isbn-verifier/src/lib.rs
+++ b/isbn-verifier/src/lib.rs
@@ -1,4 +1,20 @@
 /// Determines whether the supplied string is a valid ISBN number
 pub fn is_valid_isbn(isbn: &str) -> bool {
-    unimplemented!("Is {:?} a valid ISBN number?", isbn);
+    if isbn.len() < 10 { return false; }
+    let mut multiplier:i8 = 10;
+    let mut output = 0;
+    for char in isbn.chars(){
+        match char.to_digit(10){
+            Some(value) =>{
+                output += value * multiplier as u32;
+                multiplier -= 1;
+            },
+            None =>{
+                if char.to_ascii_lowercase() == 'x' && multiplier == 1{
+                    output += 10;
+                }
+            }
+        }
+    }
+    output % 11 == 0 && multiplier >= 0
 }
diff --git a/isbn-verifier/tests/isbn-verifier.rs b/isbn-verifier/tests/isbn-verifier.rs
index ea381c0..8f227e4 100644
--- a/isbn-verifier/tests/isbn-verifier.rs
+++ b/isbn-verifier/tests/isbn-verifier.rs
@@ -6,112 +6,94 @@ fn test_valid() {
 }
 
 #[test]
-#[ignore]
 fn test_invalid_check_digit() {
     assert!(!is_valid_isbn("3-598-21508-9"));
 }
 
 #[test]
-#[ignore]
 fn test_valid_check_digit_of_10() {
     assert!(is_valid_isbn("3-598-21507-X"));
 }
 
 #[test]
-#[ignore]
 fn test_invalid_character_as_check_digit() {
     assert!(!is_valid_isbn("3-598-21507-A"));
 }
 
 #[test]
-#[ignore]
 fn test_invalid_character_in_isbn() {
     assert!(!is_valid_isbn("3-598-P1581-X"));
 }
 
 #[test]
-#[ignore]
 #[allow(non_snake_case)]
 fn test_invalid_isbn_with_invalid_X() {
     assert!(!is_valid_isbn("3-598-2X507-9"));
 }
 
 #[test]
-#[ignore]
 fn test_valid_isbn_without_dashes() {
     assert!(is_valid_isbn("3598215088"));
 }
 
 #[test]
-#[ignore]
 #[allow(non_snake_case)]
 fn test_valid_isbn_without_dashes_and_X_as_check() {
     assert!(is_valid_isbn("359821507X"));
 }
 
 #[test]
-#[ignore]
 fn test_invalid_isbn_without_dashes_and_no_check_digit() {
     assert!(!is_valid_isbn("359821507"));
 }
 
 #[test]
-#[ignore]
 fn test_invalid_isbn_without_dashes_and_too_long() {
     assert!(!is_valid_isbn("3598215078X"));
 }
 
 #[test]
-#[ignore]
 fn too_short_isbn() {
     assert!(!is_valid_isbn("00"));
 }
 
 #[test]
-#[ignore]
 fn test_invalid_isbn_without_check_digit() {
     assert!(!is_valid_isbn("3-598-21507"));
 }
 
 #[test]
-#[ignore]
 fn test_valid_digits_invalid_length() {
     assert!(!is_valid_isbn("35982150881"));
 }
 
 #[test]
-#[ignore]
 fn test_special_characters() {
     assert!(!is_valid_isbn("!@#%!@"));
 }
 
 #[test]
-#[ignore]
 #[allow(non_snake_case)]
 fn test_invalid_isbn_with_check_digit_X_instead_of_0() {
     assert!(!is_valid_isbn("3-598-21515-X"));
 }
 
 #[test]
-#[ignore]
 fn empty_isbn() {
     assert!(!is_valid_isbn(""));
 }
 
 #[test]
-#[ignore]
 fn input_is_9_characters() {
     assert!(!is_valid_isbn("134456729"));
 }
 
 #[test]
-#[ignore]
 fn invalid_characters_are_not_ignored() {
     assert!(!is_valid_isbn("3132P34035"));
 }
 
 #[test]
-#[ignore]
 fn too_long_but_contains_a_valid_isbn() {
     assert!(!is_valid_isbn("98245726788"));
 }