misleading with the homework

Everyday David gets his homework.
One of the episodes of our daily life:
I see:
8 - 3 - 0 - 10
4 - 7 - 6 - 1
Straigh away I demande from him to solve the problems!
So, he begins to solve them step by step (without my help! but with the help of fingures):
8 - 3 = 5
5 - 0 = 5
5 - 10 = -5
Writes: 8 - 3 - 0 - 10 = -5
4 - 7 = -3
-3 - 6 = -9
-9 - 1 = -10
Whites: 4 - 7 - 6 - 1 = -10
I am very pleased with him.
About 2 hours later, I am beginnig to think that it was wierd to give such a homework in CP1. So I have decided to look again and to read the assignment (for the first time).
And the assignment sounds like:
Range les nombres du plus petit au plus grand: 8 - 3 - 0 - 10
Range les nombres du plus grand au plus petit: 4 - 7 - 6 - 1
Do you have any idea how bad I felt, when I realized that I have not even bothered to read the assigment but mislead the poor kid.
Well, he did it correctly anyway, but right now he is in the stage where he thinks that he is 100% right (which he is, in this case), but the other students in his class think that there is nothing above or below 0 to 10.