[LON-CAPA-users] formularesponse: Unable to understand formula???

[jensen]

When I try to enter answers for formula response questions, I frequently 
get the following message back fro the system:

"Unable to understand formula"

-Rven when I enter the answer exactly listed as the answer in the
"Answer for Part:0" below the Submit button.

I have icluded the example below. When I enter the answer for seed 
1034915668, I get the above message. What is going on here?

Lars.

------------------
<problem>
<script type="loncapa/perl">$sign = &random(-1,1,2);
$absslope = &random(1,9,1);
$slope = $sign*$absslope;
$intercept = &random(-10,10,1);
$ans = "$slope*x+$intercept";

</script>
<startouttext />What is the equation of a line with slope $slope and 
y-intercept $intercept ?<endouttext />
<formularesponse samples="x@-1,1#10" id="11" answer="$ans">
     <responseparam name="tol" type="tolerance" description="Numerical 
Tolerance" default=".0001" />
     <textline size="50" />

</formularesponse>

</problem>