STACK question 2+2=?

STACK question 2+2=?

by Peter Halverson -
Number of replies: 5

Hello,

I am a physics teacher attempting to use STACK to make my students analyze lab data.

As a baby step towards that goal,  I decided to make a question that asks the student 2+2=?

I used "Answer test=NumRelative" and the tolerance set to 0.

And, yes it works.  BUT, if the student gets cheeky, he can answer "3+1" or "sqrt(16)" and it will be "correct."  I don't want that.  I want the answer to be just 4.

So....  I'm guessing that the problem lies with "simplification."  I want to turn that off.  After all, look at this maxima dialog:

(%i15) is (2+2=sqrt(16));
(%o15)                               true
(%i16) simp:false;
(%o16)                               false
(%i17) is (2+2=sqrt(16));
(%o17)                               false

So in the STACK question form I turned "Auto-simplify" to "No" at the top of prt1.  And I also did that for "Question-level simplify".

But that didn't fix the problem.  How can I really turn off simplification?  Or am I missing something else?

Thank you,

Peter Halverson

PS:  I am using Moodle 2.4.9 and I installed qtype_stack_moodle26_2014011500.zip.  Maxima 5.23.2

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In reply to Peter Halverson

Re: STACK question 2+2=?

by Kees Koopman -

Hi,

That question is my question too.

An other question.

I declare two variables: "l" and "b". "l" is the lenght of a square, "b" is the width of a square. The outline is l+l+b+b.

Or 2*l+2*b or 2*(l+b).

I ask the student two questions: Write down a formula and Write down the correct answer.

How do i test if the student use a correct formula?

How do ik give points for a specific formula?

Kees

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In reply to Peter Halverson

Re: STACK question 2+2=?

by Christopher Sangwin -
Picture of Particularly helpful Moodlers Picture of Plugin developers

Thanks for posting these questions as they are central to the design of STACK!

STACK is designed to establish mathematical properties, such as "equivalence". Unfortunately this word has a number of different meanings, which are potentially confused. So, I have written some Maxima code to provide the teacher with "answer tests" which help establish if two expressions are equivalent in a number of different senses.

One sense it "algebraic equivalence" which basically tests if the difference evaluates (aka "simplifies") to zero.

A very useful sense is "up to commutativity and associativity of addition and multiplication, together with their inverses minus and division"? For example \[a+b=b+a\mbox{,}\] but \[x+x\neq 2x\mbox{.}\] This is very useful in elementary algebra, where we want the form of the answer exactly. Simplification is automatically switched off when this test is applied, otherwise it makes no sense. This is basically the case you describe.

The tests are described in
https://github.com/maths/moodle-qtype_stack/blob/master/doc/en/Authoring/Answer_tests.md

It is very unusual to only check one property. Unfortunately teachers are used to making many different and subtle judgements, and it is difficult to begin with to articulate exactly what you want. E.g. you might want both

  • equivalence with the correct answer
  • in a particular form (e.g. factored)

How to use more than one test, and link them together is described in the authoring guide.

https://github.com/maths/moodle-qtype_stack/blob/master/doc/en/Authoring/Authoring_quick_start.md

I make no apologies that STACK is complex. It has a complex task to do. I'm very open to suggestions of how to improve the system and the documentation, and very much welcome contributions. If something isn't clear to you, please let me know. I forget what people don't know. I think all teachers do this from time to time!

I also replied to a similar formulation of this question in the quiz forum earlier...
https://moodle.org/mod/forum/discuss.php?d=258632

Chris
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In reply to Christopher Sangwin

Re: STACK question 2+2=?

by Andreas Schneider -

Dear Chris


I'm trying to ask the following question with STACK:

simplify 8*x+6*x-(4*x+2*x). The Result I'm looking for is 8*x. The problem is that by typing in 8*x+6*x-(4*x+2*x) -(the question itself)- the students get the full marks.


Is there a way that 8*x+6*x-(4*x+2*x) as an answer gives zero points and 8*x gives 1 point?


I'm aware that there are answer tests and I have worked my way through the authoring guide. I have tried almost every possible combination and yet I must have forgotten the proper one. Could you please help me?


Thank you very much!


Andreas

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In reply to Andreas Schneider

Re: STACK question 2+2=?

by Tim Hunt -
Picture of Core developers Picture of Documentation writers Picture of Particularly helpful Moodlers Picture of Peer reviewers Picture of Plugin developers

You almost certainly want the answer test 'EqualComAss'. That is equal up to commutativity and associativity, so if you compare the student answer to 8*x, only 8*x and x*8 will be allowed.

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In reply to Tim Hunt

Re: STACK question 2+2=?

by Andreas Schneider -

Thank you very much! Everything is working fine now. 'EqualComAss' is perfect for that purpose.

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