Quiz

Hi:
Sorry but I can't reproduce what I want. The Poly function works fne but I don't know how works with it at answer word.
Let me explain what a wnat to dos, perhaps it more easy that I imagine.

I want that my students write algebraic formulas.

I create the following question:
--> Write a number plus 5
And the students must answer:
--> x + 5

This is easy. I can make
#Random variables
z = shuffle([1:18]);

# Question
--> Write a number plus {z}


# Answer
Type = Algebraic
Answer = ["x+z]"
Error abs < 0.1
Local variable = x={3};

Everything OK!

The problem arises with negative numbers,
With the Dominique's suggestion we can make a list without zero.

#Random variables
z = shuffle([1:18]);

#Global variables
a = [-10:-1];
b = [2:11];
x = concat(a,b);
y = sublist(x, z);


# Question
--> Write a number plus {y}

The solution could be x-2
So:
a) I can't write the question: Write a number plus {y} because "plus" could be "minus"
b) I can't put the answer: ["x+z]" because it appears x+-2

I try make this:
#Random variables
z = shuffle([1:18]);

#Global variables
a = [-10:-1];
b = [2:11];
x = concat(a,b);
y = sublist(x, z);
z = y[0]
sig = (z <0) ? 0:1;
signo =["minus","plus"][sig];
z_abs = abs (z);

# Answer
Write a number {signo} {z_abs}

But I don't know how to correctly evaluate the answer because sometimes is "+" and sometimes is "-".

Can you help me?

Thanks in advanced.