Percentage Progress from multiple sources which runs in sequence.

Program.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Threading;

namespace ConsoleApp7
{
    public class MainProgressReporter : IProgress<double>
    {
        public void Report(double value) => Console.WriteLine(value.ToString(CultureInfo.InvariantCulture));
    }

    public class RatioAwareProgressReporter : IProgress<double>
    {
        private readonly int _alreadyMadeProgress;
        private readonly int _percentageRatio;
        private readonly IProgress<double> _progress;

        public RatioAwareProgressReporter(int alreadyMadeProgress, int percentageRatio, IProgress<double> progress)
        {
            _alreadyMadeProgress = alreadyMadeProgress;
            _percentageRatio = percentageRatio;
            _progress = progress;
        }

        public void Report(double value) => 
            _progress.Report(_alreadyMadeProgress + (_percentageRatio * value) / 100);
    }

    class Program
    {
        static void Main(string[] args)
        {
            Do(60000, new MainProgressReporter());
        }

        private static void Do(long totalLength, IProgress<double> progress)
        {
            var length1 = (long)Math.Floor(((double)(totalLength) * 25) / 100);
            var length2 = (long)Math.Floor(((double)(totalLength) * 40) / 100);
            var length3 = (long)Math.Floor(((double)(totalLength) * 35) / 100);

            DoInner(length1, new RatioAwareProgressReporter(0, 25, progress));
            DoInner(length2, new RatioAwareProgressReporter(25, 40, progress));
            DoInner(length3, new RatioAwareProgressReporter(65, 35, progress));
        }

        private static void DoInner(long length, IProgress<double> progress)
        {
            var reportedProgresses = new List<double> { 0 };
            var cts = new CancellationTokenSource(TimeSpan.FromMilliseconds(length));
            var waitAmount = length / 100;
            while (!cts.IsCancellationRequested)
            {
                var madeProgress = reportedProgresses.Last() + 1;
                progress.Report(madeProgress);
                reportedProgresses.Add(madeProgress);

                Thread.Sleep(TimeSpan.FromMilliseconds(waitAmount));
            }

            if (!reportedProgresses.Any(x => x == 100))
            {
                progress.Report(100);
            }
        }
    }
}