## WeBWorK Problems

### Re: access to student responses between evaluations

by Hedley Pinsent -
Number of replies: 0
Well here it is, for whoever has been following the discussion.
I think it is ok now. I am quite pleased with how it works.
I tried lots of stuff; this is probably the only way to do it.
The subroutines seem to make a copy everything they receive, and are very reluctant to give anything back.

Thanks - hp

## DESCRIPTION
## Statistics
## ENDDESCRIPTION

## KEYWORDS('Statistics','Confidence Intervals')
## Tagged by

## DBsubject('Statistics')
## DBchapter('Confidence Intervals')
## DBsection('Sample Size - Proportion')
## Date('')
## Author('')
## Institution('')
## TitleText1('')
## EditionText1('')
## AuthorText1('')
## Section1('')
## Problem1('')

DOCUMENT();

"PGbasicmacros.pl",
"PGnumericalmacros.pl",
"PGstatisticsmacros.pl" ,
"PGauxiliaryFunctions.pl",
"MathObjects.pl",
);

TEXT(beginproblem());
$showPartialCorrectAnswers = 1;$ppercent = random(40,80,10);
$p =$ppercent / 100;

$confidence = list_random(80,90,95,98,99);$deg = $confidence / 100;$E = list_random (1,2,3,4,5,6,8,10);
$dE =$E /100;

$z=udistr (0.5 -$deg/2);
#$ans1 =$z;

$ans2 = ceil($p*(1 - $p)*($z/$dE )**2); Context()->flags->set( tolType => 'absolute', tolerance => 0.0001 );$ans1 = $z;$ans12 = MultiAnswer( $ans1,$ans2 )->with(
singleResult => 0,
checker => sub {
my ( $correct,$student, $self ) = @_; my ($stu1, $stu2 ) = @{$student};
my $stuCalc = Compute("int(0.99999 +$p*(1 - $p)*($stu1/$dE)^2)"); my ($cor1, $cor2 ) = @{$correct};

if ( abs($cor1 -$stu1)<0.01 && ( ($stuCalc ==$stu2) || ($cor2 ==$stu2) )) {
return [1,1];
} elsif ( abs($cor1 -$stu1)<0.01 ) {
return [1,0];
} elsif ( ($stuCalc ==$stu2) || ($cor2 ==$stu2) ) {
return [0,1];
} else {
return [0,0];
}
}
);

BEGIN_TEXT

It is claimed that $ppercent$PERCENT of households now subscribe to cable TV. You would like to verify this statement for your class in mass communications. You want an estimate within $E percentage points, with a$confidence $PERCENT level of confidence.$BR
What z-value would you use?
\{ $ans12->ans_rule(25) \}$BR

How large of a sample is required? $BR \{$ans12->ans_rule(25) \} $BR $$\bar p (1 - \bar p) (\frac{z}{E})^2$$$BR Additionally we always round up. $BR END_TEXT ANS($ans12->cmp() );

ENDDOCUMENT();