diff --git a/solutions/elixir/binary-search/2/lib/binary_search.ex b/solutions/elixir/binary-search/2/lib/binary_search.ex
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+++ b/solutions/elixir/binary-search/2/lib/binary_search.ex
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+defmodule BinarySearch do
+  @doc """
+    Searches for a key in the tuple using the binary search algorithm.
+    It returns :not_found if the key is not in the tuple.
+    Otherwise returns {:ok, index}.
+
+    ## Examples
+
+      iex> BinarySearch.search({}, 2)
+      :not_found
+
+      iex> BinarySearch.search({1, 3, 5}, 2)
+      :not_found
+
+      iex> BinarySearch.search({1, 3, 5}, 5)
+      {:ok, 2}
+
+  """
+
+  @spec search(tuple, integer) :: {:ok, integer} | :not_found
+  def search({}, _), do: :not_found
+  def search(numbers, key), do: get_index(numbers, key, tuple_size(numbers) - 1)
+
+  defp get_index(numbers, key, min \\ 0, max) do
+    case min + div(max - min, 2) do
+      index when elem(numbers, index) == key -> {:ok, index}
+      index when elem(numbers, index) > key and index < max -> get_index(numbers, key, min, index)
+      index when elem(numbers, index) < key and index > min -> get_index(numbers, key, index, max)
+      _ when elem(numbers, max) == key -> {:ok, max}
+      _ -> :not_found
+    end
+  end
+end