Greetings all!

I have found a peculiar rounding problem when using the "sprint" command.

I do not think it has anything to do with absolute tolerance, but perhaps you could please shed light on this?

Let me explain:

The homework assignment below asks students to calculate Z-scores and their associated probabilities. The students are to use conventional Z-tables which require a rounding of the z-score to the second decimal and webwork is to check on this z-score value.

To round a calculation down to the second decimal I have been using the sprint command:

$zb12 =sprintf("%0.2f",$zb1);

And then converting this variable to a math object with a "Compute()" command. All was working fine until a particular student had a z-score of

Z = -1.125 Which should have rounded to Z = -1.13, but the sprint command clipped the third decimal and returned Z = -1.12

These Values fail to "round up" at the second decimal:

2.105 -1.105

2.115 -1.115

2.125 -1.125

2.135 -1.135

2.145 -1.145

2.155 -1.155

But these values will round up at the second decimal:

2.165 -1.165

2.175 -1.175

2.185 -1.185

2.195 -1.195

Is this the sprint convention?

Do you see a solution beyond the hacking "if then condition" enforcing the rounding that I put in below?

I would very much appreciate your insight as to why this rounding has not occurred.

Thanks, Tim

# DESCRIPTION Normal probability and Continuity Correction

# Find the associated probability given mu and sigma.

# Use correct notation.

# WeBWorK problem written by TimPayer <tsp1@humboldt.edu>

# ENDDESCRIPTION

## DBsubject(Probability)

## DBchapter(Random variables)

## DBsection(Expectation)

## Institution(Humboldt State University)

## Author(Tim Payer)

## KEYWORDS(probability, translate, notation)

DOCUMENT();

loadMacros(

"PGstandard.pl",

"PGunion.pl",

"PGnumericalmacros.pl",

"PGstatisticsmacros.pl",

"MathObjects.pl",

"parserPopUp.pl",

"PGML.pl",

"unionTables.pl",

"niceTables.pl",

"PGcourse.pl",

"weightedGrader.pl"

);

install_weighted_grader();

#Text(beginproblem()); #uncomment

#install_problem_grader(~~&std_problem_grader);

$showPartialCorrectAnswers = 1;

Context("Numeric");

Context()->flags->set(

tolerance => 0.0001,

tolType => "absolute",

);

$tree = list_random('redwood', 'Douglass-fir', 'grand-fir', 'Western hemlock','tanoak','madrone');

$m = random(35,39,0.1);

$ls = floor($m/9) + 0.1;

$hs =ceil($m/4)- 0.3;

$s = random($ls, $hs, 0.1);

## These Do loops are just to insure decimal answers that exceed four

## decimals and thus will prompt the student round correctly before

## drawing a Z-table value.

#do { $a = random(0.1,1.9,0.1); } until (floor(10000*$a/$s) < 10000*$a/$s);

#do { $l = random(0.1,1.9,0.1); } until (floor(20000*$l/$s) < 20000*$l/$s);

$l = random(0.1,1.9,0.1);

$a = random(0.1,1.9,0.1);

$ax = floor($m-$a);

$bx = ceil($m+2*$l);

$axcc = $ax -0.5;

$bxcc = $bx +0.5;

$zxls = ($axcc - $m)/$s;

$zxus =($bxcc - $m)/$s;

$zxl2 =sprintf("%0.2f",$zxls);

$zxu2 =sprintf("%0.2f",$zxus);

$pxs = normal_prob($zxl2, $zxu2, mean=>0, deviation=>1);

$px =sprintf("%0.4f",$pxs);

## Problem 8.1a ##

$a1 = floor($m-1.2*$s);

$a1cc = $a1 -0.5;

$za = ($a1cc - $m)/$s;

$popup1 = PopUp(

["Choose:", "Y =", "Y <", "Y < or =", "Y >", "Y > or ="], "Y > or =");

$popup2 = PopUp(

["Choose:", "Y =", "Y <", "Y < or =", "Y >", "Y > or ="], "Y > or =");

$ans1 =Compute("$a1cc");

$popup3 = PopUp(

["Choose:", "Z =", "Z <", "Z < or =", "Z >", "Z > or ="], "Z > or =");

$za2 =sprintf("%0.2f",$za);

$ans2 = Compute("$za2");

$pa = normal_prob($za2, infty, mean=>0, deviation=>1);

$ans3 = Compute("$pa");

## Problem 8.1b ##

$b1cc = $a1cc;

$b2cc = $a1 +0.5;

$zb1 = ($b1cc - $m)/$s;

$zb2 = ($b2cc - $m)/$s;

$popup4 = PopUp(

["Choose:", "Y =", "Y <", "Y < or =", "Y >", "Y > or ="], "Y =");

$popup5 = PopUp(

["Choose:", $a1-1.5, $a1-1,$a1-0.5, $a1, $a1+0.5,$a1+1,$a1+1.5], $a1-0.5);

$popup6 = PopUp(

["Choose:", "= Y =", "< Y <", "< or = Y < or =", "= Y < or =", "< or = Y ="], "< or = Y < or =");

$popup7 = PopUp(

["Choose:", $a1-1.5, $a1-1,$a1-0.5, $a1, $a1+0.5,$a1+1,$a1+1.5], $a1+0.5);

$popup8 = PopUp(

["Choose:", "= Z =", "< Z <", "< or = Z < or =", "= Z < or =", "< or = Z ="], "< or = Z < or =");

$zb12 =sprintf("%0.2f",$zb1);

$zb22 =sprintf("%0.2f",$zb2);

$ans4 =Compute("$zb12");

$ans5 =Compute("$zb22");

## Enforcing rounding to the second decimal loop?###

$dif5 =abs($ans5 -$zb2);

if(($dif5 > 0.005) || ($dif5 == 0.005)){

if($ans5 < 0){

$ad = Compute("$ans5-.01");

$ans5 =$ad;

} elsif($ans5 > 0 ) {

$ad = Compute("$ans5+.01");

$ans5 =$ad;

} else {

$sw = $ans5;

$ans5 = $sw;

}

}

$tes1 = Compute("-1.125");

$test1 =sprintf("%0.2f",$tes1);

####################

$pb = normal_prob($zb12, $ans5, mean=>0, deviation=>1);

$ans6 =Compute("$pb");

## Problem 8.1c ##

$c2= floor($m+0.8*$ka);

$c1cc = $a1cc;

$c2cc = $c2 +0.5;

$zc1 = ($c1cc - $m)/$s;

$zc2 = ($c2cc - $m)/$s;

$popup9 = PopUp(

["Choose:", "= Y =", "< Y <", "< or = Y < or =", "= Y < or =", "< or = Y ="], "< or = Y < or =");

$popup10 = PopUp(

["Choose:", $a1-1.5, $a1-1,$a1-0.5, $a1, $a1+0.5,$a1+1,$a1+1.5], $a1-0.5);

$popup11 = PopUp(

["Choose:", "= Y =", "< Y <", "< or = Y < or =", "= Y < or =", "< or = Y ="], "< or = Y < or =");

$popup12 = PopUp(

["Choose:", $c2-1.5, $c2-1,$c2-0.5, $c2, $c2+0.5,$c2+1,$c2+1.5], $c2+0.5);

$popup13 = PopUp(

["Choose:", "= Z =", "< Z <", "< or = Z < or =", "= Z < or =", "< or = Z ="], "< or = Z < or =");

$zc12 =sprintf("%0.2f",$zc1);

$zc22 =sprintf("%0.2f",$zc2);

$ans7 =Compute("$zc12");

$ans8 =Compute("$zc22");

$pc = normal_prob($zc12, $zc22, mean=>0, deviation=>1);

$ans9 =Compute("$pc");

#######

$column1 = PGML::Format2(<<'END_PGML');

*Drawn from Lecture Notes: Week 5 Day 1.*

*8.2)* In genetic studies of the fruit-fly _Drosphila melanogaster_, one variable of interest is the total number of bristles on the dorsal surface of the mesothorax. For a certain _Drosphila_ population, this bristle count follows a normal distribution with a mean of [`\mu`] = [``[$m]``] and a standard deviation of [`\sigma`] = [``[$s]``]. Find the following probabilities by accounting for the continuity correction.

Let [`Y`] = The total number of bristles on the dorsal surface of the mesothorax of a randomly drawn fruit fly _Drosphila_ population.

*8.2a)* Find the probability of drawing a fruit fly with [``[$a1]``] or more bristles on the dorsal surface of the mesothorax.

[``\Large{P(}``] [$popup1->menu]* [``\Large{[$a1]) \approx}``]

[``\Large{\approx P(}``] [$popup2->menu]* [____] [``\Large{) \, \approx }``]

[``\Large{\approx P(}``] [$popup3->menu]* [____] [``\Large{) \, \approx }``] [____]

*8.2b)* Find the probability of drawing a fruit fly with [$a1] bristles on the dorsal surface of the mesothorax.

[``\Large{P(}``] [$popup4->menu]* [``\Large{[$a1]) \approx}``]

[``\Large{\approx P(}``] [$popup5->menu]* [$popup6->menu]* [$popup7->menu]*[``\Large{) \, \approx}``]

[``\Large{\approx P(}``] [____] [$popup8->menu]* [____] [``\Large{) \, \approx }``] [____]

*8.2c)* Find the probability of drawing a fruit fly that has between [$a1] and [$c2] bristles (inclusive) on the dorsal surface of the mesothorax.

[``\Large{P([$a1] }``] [$popup9->menu]* [``\Large{[$c2]) \approx}``]

[``\Large{\approx P(}``] [$popup10->menu]* [$popup11->menu]* [$popup12->menu]*[``\Large{) \, \approx}``]

[``\Large{\approx P(}``] [____] [$popup13->menu]* [____] [``\Large{) \, \approx }``] [____]

END_PGML

$column2 =$BCENTER."Magnified images of the 'wild type' $BITALIC Drosphila melanogaster $EITALIC".image("drosophilandi_F.png", width=>343, height=>277, tex_size=>700).$BR." ".$BR.image("drosophilandi_M.png", width=>320, height=>355, tex_size=>700).$BR." ".$BR.image("drosophilandi_C.png", width=>213, height=>250, tex_size=>700).$BR."All images courtesy of www.drosphilandi.com".$BR.$BR.$ECENTER;

TEXT(ColumnTable($column1,$column2));

########

BEGIN_PGML

*Notation Notes:*

Using a combination of popup displays and numerical entries, present your answers in the form laid out in the row table below. Adjust the real world variable of bristle counts according to the English description for an inclusive inequality and the correct continuity correction. Please note that the "popup" answers used in webwork cannot accommodate the inclusive inequalities of [`\le`] and [`\ge`]. These inequalities will have to be expressed with [`(< or =)`] and [`(> or =)`]. For example, if given the question "Find the probability of drawing a fruit fly that has a total bristle count between [$ax] and [$bx] bristles (inclusive) on the dorsal surface of the fruit fly's mesothorax." Then your answer would take the following form:

END_PGML

BEGIN_TEXT

$PAR

\{

DataTable(

[

[['Use the real world variable, \(Y\), within probability notation as your first translation from text to notation:'],' \(P( $ax \le Y \le $bx ) \) '],

[[' Adjust the bounded regions using inclusive inequalities and the continuity correction. ' ],' \(\approx P( $axcc \le Y \le $bxcc ) \)'],

[[ 'Convert these adjusted real world values into the closest second decimal Z-scores.'], ' \( \approx P( $zxl2 \le Z \le $zxu2 ) \)'],

[[ 'Calculate the probability with fourth decimal accuracy:'],' \(\approx $px \)']

],

caption => 'Adjust the real-world values for the continuity correction and then use Z-score probability notations to calculate the probability.',

midrules => 1,

align => '|p{5in}|p{1.8in}| ',

);

\}

$PAR

END_TEXT

#Adapted weighted answers values:

## Problem 8.2a ##

WEIGHTED_ANS( ($popup1)->cmp, 2 );

WEIGHTED_ANS( ($popup2)->cmp, 2 );

WEIGHTED_ANS( ($ans1)->cmp, 7 );

WEIGHTED_ANS( ($popup3)->cmp, 2 );

WEIGHTED_ANS( ($ans2)->cmp, 7 );

WEIGHTED_ANS( ($ans3)->cmp, 8 );

## Problem 8.2b ##

WEIGHTED_ANS( ($popup4)->cmp, 2 );

WEIGHTED_ANS( ($popup5)->cmp, 7 );

WEIGHTED_ANS( ($popup6)->cmp, 2 );

WEIGHTED_ANS( ($popup7)->cmp, 7 );

WEIGHTED_ANS( ($ans4)->cmp, 7 );

WEIGHTED_ANS( ($popup8)->cmp, 2 );

WEIGHTED_ANS( ($ans5)->cmp, 7 );

WEIGHTED_ANS( ($ans6)->cmp, 7 );

## Problem 8.2c ##

WEIGHTED_ANS( ($popup9)->cmp, 2 );

WEIGHTED_ANS( ($popup10)->cmp, 7 );

WEIGHTED_ANS( ($popup11)->cmp, 2 );

WEIGHTED_ANS( ($popup12)->cmp, 7 );

WEIGHTED_ANS( ($ans7)->cmp, 7 );

WEIGHTED_ANS( ($popup13)->cmp, 2 );

WEIGHTED_ANS( ($ans8)->cmp, 7 );

WEIGHTED_ANS( ($ans9)->cmp, 7 );

BEGIN_PGML_SOLUTION

The correct answers are coming....in 2017, Hah!

Without context:

zb1 = [$zb1]

zb2 = [$zb2]

With context at second decimal:

zzb1 = [$zzb1]

zzb2 = [$zzb2]

tes1 = [$tes1]

test1 = [$test1]

dif = [$dif]

dif5 = [$dif5]

zb22 = [$zb22]

zb = [$zb]

ans5 = [$ans5]

ans6 = [$ans6]

END_PGML_SOLUTION

ENDDOCUMENT();