However nothing seems to be acceptable to enter this into the answer blank. Entering [5.099] gives the message:

Your answer isn't an interval, set or union

(it looks like a real number)

And entering [5.099, 5.101] gives the message:

The parentheses for your set are of the wrong type

What's going on here?

For now I will advise the author to tighten the tolerance, and I think all will be well. But I wanted to post in case this identifies a bug.

DOCUMENT(); loadMacros( "PGstandard.pl", "MathObjects.pl", "PGML.pl", ); ############################################## TEXT(beginproblem()); $a = 5.1; $b = 0.001; Context("Interval"); $c = $a-$b; $d = $a+$b; $ans = Compute("[$c,$d]"); ############################################## BEGIN_PGML Enter [`[$ans]`]. [_______________]{$ans} END_PGML ############################################## ENDDOCUMENT();