open System

​

let sumEcts courseSet courseBase =

    let isPartOfCourseSet cn _ =

        courseSet |> Set.contains cn

​

    courseBase

    |> Map.filter isPartOfCourseSet

    |> Map.toSeq

    |> Seq.map (fun(cn, cd)->cd)

    |> Seq.sum

​

let courseBase =

    [

        (11111, 11)

        (22222, 22)

        (33333, 33)

        (44444, 44)

        (55555, 55)

    ]

    |> Map.ofList

​

let courseSet =

    [11111; 22222; 33333 ]

    |> Set.ofList

​

courseBase 

|> sumEcts courseSet

|> Console.WriteLine