Tony Gardner-Medwin
Posts: 14
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| 30/05/2007 12:58 |
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Hi Madan, The choices about how to give feedback and diagnosing where students have gone wrong is really more to do with how sophisticated your software is, and how much effort you want to put into devising good answer checking, than it is to do with CBM. With CBM it is, however, particularly valuable to give immediate feedback while the student is still thinking about why they may feel sure or uncertain that they have the right answer. The LAPT software for CBM is actually quite sophisticated, and can give appropriate explanations for specific correct answers ( A() below ) or incorrect answers ( I() below ). It can also base mathematical questions on randomised input values, if you wish - though I don't do this in the following example, which defines ranges of allowable values and variations of unit spelling in the answers, and chastises the student (though marking them correct) for inappropriate precision or lack of units. Insufficient precision, wrong units, and a comon error in working are each picked up and marked wrong. I seldom go to this kind of trouble in wriiting Qs, since a student trying to learn can usually identify their error by reading a simple explanation, as at the end here.
Q("Convert 5.23 miles to km.");
A("8.42 km"); // model answer
A("{8.4168 8.4i69} *","Yes, but since the distance was only given to 3 significant figures, you have given an inappropriately precise answer");
A("{8.41 8.43} km kilom* ","Good answer!"); //accepts km as unit, or anything starting kilom
A("{8.41 8.43} ","Yes, but you really should have included the units.");
I("{8.41 8.43} * ","The units should be km.");
I("{8.4 8.5} *","You haven't given the answer accurately enough");
I("{3.2 3.3} *","No. You have used the conversion factor (0.6214 km/mi) the wrong way round.");
E("The conversion factor is 0.62137 mi/km. So 5.23 mi = 5.23 / 0.62137 mi * (km/mi) = 8.42 km, to 3 s.f.");
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