## 2017 Problem Authoring Workshop

### Problems which ask for examples

by Oscar Levin -
Number of replies: 2
This is probably an advanced topic, but I ran into it while writing problems for week 1 homework. The specific problem I want to write is this:

"Give an example of sets A and B with |A| = 4, |B| = 6, and |A U B| = 8."

Of course there are infinitely many correct answers, but I should be able to check whether an answer is correct. To do so though, I would need to take the student's answer run some code on it (perhaps, if len(A) == 4 && len(B) == 6 && len(union(A,B)) == 8, return true; where I might need to define the union function, depending on what perl knows how to do already).

### Re: Problems which ask for examples

by Gavin LaRose -
Hi Oscar,

We'll be talking about this more in the next week or so. The short answer is that we want to use a custom checker (see http://webwork.maa.org/wiki/CustomAnswerCheckers) for this type of thing to find the student's answer and determine that it's correct.

Gavin

### Re: Problems which ask for examples

by Davide Cervone -
To be able to work with several answers at once, you need to use the MultiAnswer object available in the parserMultiAnswer.pl macro file. You get access to the student answers through the custom checker function that you provide. See the MultiAnswer documentation for details.

Here is an example of how to do this:

loadMacros(
"PGstandard.pl",
"MathObjects.pl",
"PGML.pl",
$A = Compute("{1,2,3,4}");$B = Compute("{3,4,5,6,7,8}");
$ma = MultiAnswer($A,$B)->with( singleResult => true, format => "A = %s and B = %s", tex_format => "A = %s\hbox{ and }B = %s", checker => sub { my ($correct, $student,$m, $ans) = @_; my ($A, $B) = @$student;
if (!$ans->{isPreview}) { Value->Error("A doesn't have 4 elements") if$A->length != 4;
Value->Error("B doesn't have 6 elements") if $B->length != 6; Value->Error("The union doesn't have 8 elements") if ($A + $B)->length != 8; } return$A->length == 4 && $B->length == 6 && ($A + $B)->length == 8; } ); BEGIN_PGML Give an example of sets [A] and [B] of numbers with [|A| = 4], [|B| = 6], and [|A \cup B| = 8]. >> [A] = [______________]{$ma} and [B] = [_______________]{\$ma}  <<