## WeBWorK Problems

### Message "Your union can be simplified by combining some sets" in case if a wrong answer. ### Message "Your union can be simplified by combining some sets" in case if a wrong answer.

by F. Heiderich -
Number of replies: 1
In the following problem the student gets the message "Your union can be simplified by combining some sets" if he enters the wrong answer "(-inf,-3) U (1,inf)". In my opinion this is misleading, because it suggests that the answer is right but could be further reduced. Neither of it is the case.

DOCUMENT();
"PGstandard.pl",
"PGML.pl",
"MathObjects.pl",
"PG.pl",
"PGbasicmacros.pl",
"PGcourse.pl",
);

TEXT(beginproblem());

Context("Interval");

$I1 = Interval("(-infinity,-3)");$I2 = Interval("(1,infinity)");
$I1intI2 =$I1->intersect($I2); BEGIN_PGML This problem will produce the error message 'Your union can be simplified by combining some sets' when the wrong answer "(-inf,3) U (1,inf)" is entered. Determine the set of all [x \in \mathbb{R}] that fulfill the condition [x < -3 \text{ and } x > 1]: [_______________]{"$I1intI2"}.

END_PGML

ENDDOCUMENT(); 