Upon trying in simple Console App, with a code like the following, the result found to be quite something unexpected as per the clip following in the end. Code Used

double A = 1234567.8991;
Console.WriteLine(Convert.ToString(A));
Console.WriteLine(Convert.ToString(A - Math.Truncate(A)));
Console.WriteLine(Convert.ToString(A - Math.Floor(A)));

Any reason for the said 0.899100000038743 appearing so as follows?

Since, it was only 0.8991, that was expected!