diff --git a/modules/09_cpp11/src/auto_and_range_for.cpp b/modules/09_cpp11/src/auto_and_range_for.cpp
index 7830dc8..6d809ca 100644
--- a/modules/09_cpp11/src/auto_and_range_for.cpp
+++ b/modules/09_cpp11/src/auto_and_range_for.cpp
@@ -1,20 +1,26 @@
 #include "auto_and_range_for.hpp"
 
+#include <algorithm>
+
 namespace cpp11 {
 
 auto double_values(const std::vector<int>& input) -> std::vector<int> {
-    (void)input;
-    return {};
+    auto result = std::vector<int>{};
+    result.reserve(input.size());
+    std::ranges::for_each(input, [&result](const int value) { result.push_back(value * 2); });
+    return result;
 }
 
 auto join_with_auto(const std::vector<std::string>& parts) -> std::string {
-    (void)parts;
-    return {};
+    auto result = std::string{};
+    std::ranges::for_each(parts, [&result](const std::string& part) { result += part; });
+    return result;
 }
 
 auto count_if_positive(const std::vector<int>& input) -> int {
-    (void)input;
-    return 0;
+    auto count = 0;
+    std::ranges::for_each(input, [&count](const int value) { if (value > 0) ++count; });
+    return count;
 }
 
 }  // namespace cpp11