Student to mark a question as "impossible"

[Antony Edwards]

Hi all,

I am writing a series of questions on the theme of  "give an example of <object> satisfying <condition>". These questions are generally not for course credit; the main benefit of adding these to Numbas is that students can trial their answers, rather than requiring feedback from tutors. Of the questions we regularly use, several are actually impossible combinations of properties for that object. I am looking for a good way for a student to mark these as such.

What would be fabulous would be a tick box with "this part is impossible", but I think that might be aiming the bar a little high! A lower-goal would be to give the students the instructions "leave the question blank if you think the combination is impossible". For matrix parts, I assume that I would need to modify the "any_empty" part of the matrix marking algorithm to mark as correct when it was all empty? -- could anyone suggest how I might do this please?

Is there a universal way of doing this for all part types?

Cheers,

Ant.

[Julia Goedecke]

The way I've done this before is to use mathematical expressions and ask the students to put "NA" if it doesn't exist. This would not work for matrices though. I've done it for linear combinations, ie where I've has to enter the coefficients. I can find the question tomorrow and send if you're interested.

You can do it in different ways too though i suppose. You could put a "choose one from a list" with "possible or impossible", and maybe one could do a marking algorithm which gives full marks when impossible even if other gaps are empty. Have not tried this. Or you do explore mode and do separate parts, first where they say possible or impossible, and if possible, the one where you actually put the example in comes up. 

Julia 

--
You received this message because you are subscribed to the Google Groups "Numbas Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to numbas-users...@googlegroups.com.
To view this discussion on the web, visit https://groups.google.com/d/msgid/numbas-users/d9eb6a33-6393-4a85-a8e6-aff58d8c91f0n%40googlegroups.com.

[Christian Lawson-Perfect]

I did this recently for one of our exams, where the student was shown some combinations of dot and cross product, and asked to give explicit values after substituting in given vectors, if the result is defined. I used explore mode to first ask the student which expressions were defined, and if so whether they're scalars or vectors, then in turn ask for either a scalar or a vector for each expression.

When the answer is always the same type if it exists, I like the idea of a tickbox for "this is impossible" next to the input. I've made an example at https://numbas.mathcentre.ac.uk/question/87350/tick-box-for-this-is-impossible/

To view this discussion on the web, visit https://groups.google.com/d/msgid/numbas-users/CAK1uihtL6uxWyf3T-SJ6Nhq4W5n%3DOr3YW7%2BFSt_rzNF7_QeAWw%40mail.gmail.com.

[Antony Edwards]

That's a great solution - thanks Christian. 

Cheers,

Ant.

[Antony Edwards]

Hi Christian,

I've tried to adapt your example but I've run into problems. I think the issue is because the correct example Gap0 condition is located in the custom marking algorithm for the Part, but my question has these in the Gap itself. I've tried replicating them where you had yours but the question won't work.

My question is at: https://numbas.mathcentre.ac.uk/question/87325/give-an-example-of-vectors-1/. Part a is possible, and Part b is impossible.

Thanks in advance,

Ant.

On Thursday, January 21, 2021 at 8:55:39 PM UTC+11 christia...@gmail.com wrote:

[Julia Goedecke]

Hello,
I just used Christian's "tick if impossible" question to do a similar
thing with a matrix entry rather than number entry. It turns out there
is a complication which it took me 2h to find, so I thought I'd share it
to spare anyone else the 2h!

https://numbas.mathcentre.ac.uk/question/share/view/d9a1a7a5-24c0-494e-9173-45a1c3e87aa5

A question for Christian: why is there a difference between the bit
where you can test the marking algorithm underneath, and when you
actually test run it? What I came across is that it saves an empty
matrix entry as [[safe""]] instead of empty, but testing it underneath
the marking algorithm did not pick this up. It only occurred when I
actually test ran it.

Julia

> <mailto:numbas-users...@googlegroups.com>.

> To view this discussion on the web, visit
> https://groups.google.com/d/msgid/numbas-users/d9eb6a33-6393-4a85-a8e6-aff58d8c91f0n%40googlegroups.com

> <https://groups.google.com/d/msgid/numbas-users/d9eb6a33-6393-4a85-a8e6-aff58d8c91f0n%40googlegroups.com?utm_medium=email&utm_source=footer>.

>
> --
> You received this message because you are subscribed to the Google
> Groups "Numbas Users" group.
> To unsubscribe from this group and stop receiving emails from it,
> send an email to numbas-users...@googlegroups.com

> <mailto:numbas-users...@googlegroups.com>.

> To view this discussion on the web, visit

> https://groups.google.com/d/msgid/numbas-users/CAK1uihtL6uxWyf3T-SJ6Nhq4W5n%3DOr3YW7%2BFSt_rzNF7_QeAWw%40mail.gmail.com
> <https://groups.google.com/d/msgid/numbas-users/CAK1uihtL6uxWyf3T-SJ6Nhq4W5n%3DOr3YW7%2BFSt_rzNF7_QeAWw%40mail.gmail.com?utm_medium=email&utm_source=footer>.

>
> --
> You received this message because you are subscribed to the Google
> Groups "Numbas Users" group.
> To unsubscribe from this group and stop receiving emails from it, send
> an email to numbas-users...@googlegroups.com

> <mailto:numbas-users...@googlegroups.com>.

> To view this discussion on the web, visit

> https://groups.google.com/d/msgid/numbas-users/CAEMHSOi_wZ51bYtXreVaciobGmgQ%3D%2B6k3um0Sqdo%3DyE6j65H2Q%40mail.gmail.com
> <https://groups.google.com/d/msgid/numbas-users/CAEMHSOi_wZ51bYtXreVaciobGmgQ%3D%2B6k3um0Sqdo%3DyE6j65H2Q%40mail.gmail.com?utm_medium=email&utm_source=footer>.

--

Dr Julia Goedecke
Teaching Fellow in Mathematics
University of Leicester


https://www.ipetitions.com/petition/mathematics-is-not-redundant