Hackerrank optimizing euler problem #1

Hello everyone,

I spent my weekend optimising the first problem and learned allot in the process about Elixir. I got to 80 points, but still the third hidden test is timing out. Can anyone take a look at the code bellow and give me some pointers on how to improve the performance of the algorithm?

Problem is here

You can find the solution bellow; notice that I tried to parallelise as much as I could where it made sense (i.e. the solution is being computed as you input the numbers, in parallel). I don’t have allot of experience with Elixir so I would appreciate a helping hand.

defmodule Solution do

  def calculateFinalSum([{:ok, a}, {:ok, b}, {:ok, c}]) do
    a+b-c
  end

  def dividedSum(n, dividend) do
    p = div(n-1, dividend)
    div(dividend * p * (p+1), 2)
  end

  def solveOne(n) do
    {number, _} = Integer.parse(n)
    Task.async_stream([3,5,15], &(Solution.dividedSum(number, &1)))
    |> Enum.to_list
    |> Solution.calculateFinalSum
  end

  def solve() do
      IO.gets("")
      IO.stream(:stdio, :line)
        |> Task.async_stream(&(Solution.solveOne(&1)))
        |> Enum.each(fn {:ok, n} -> IO.puts(n) end)
  end
end

Solution.solve