Answer:

1000.0. The variable starts out at 0.0, and has 0.1 added to it until it reaches 999.9. The while allows one more iteration, so 0.1 is added to make 1000.0. The loop now exits.

But if you try this the variable actually ends up as 1000.0000000001588.

End of the Chapter

I hope you were not counting on more, because this is the end of the chapter. You may wish to review the following.

Counting upwards by two.
Loop condition as a gatekeeper
Iteration
Decrementing the Loop Control Variable.
An Infinite Loop.
Why the Loop Control Variable should be an integer.

You have reached the end of the chapter.