Well if you get back to the definition of a division, diving X by Y is finding out how many Ys you can have in a X.
It is clear that you will have more than X times Y if Y is less than 1 since dividing X by 1 is exactly X.
If you think of 10 and 1, you can divide 10 in exactly 10 portions of 1.
But you can divide it into 100 portions of 0,1.
And 100 is bigger than 10 of course.
Hope this helps.
the answer is 2.236 units
Subtract 5 each play so go backwards from zero and you should finish at -15