This can happen for a number of reasons, but the primary two reasons are:

    a. EVTG cannot find a value for one or more of the variables satisfying the given conditions.

    b. One or more of the algorithm definitions does not make sense.

The first sign of trouble is when we press Record, EVTG takes a long time to return to the question bank.  That is because it is going through all of the possible values without success.

An example of the (a).

In this question bank, while working on question 2, at one time we had the following list of algorithm definitions:

After pressing Record, EVTG took a long time to return to the question bank and then our question appeared with ?? in place of every variable.

Because we had used the definitions for a, b and p and the condition on b in a previous question bank (Chapter 1), we looked for problems in the answer variables.  Looking carefully at AnsC (blue background), we saw that instead of 

          AnsC= round(b*p/100,1) 

   we had typed 

        AnsC= round(b*100/p,1) or AnsC=a=AnsA.

Since our condition on the answers requires that they are all different, obviously EVP could not find any values satisfying this condition and thus replaced all the variables with ??.

An example of (b).

While working on question 4 of the same bank, we had the following algorithm definition list:

At first we assumed we had an inconsistent definition. Then we saw that we had spelled the function name “choose” incorrectly and EVP was looking (unsuccessfully) for a definition of a function “chose”. This same problem will occur if we type the name of a variable incorrectly. Capital and small letters have no effect – we just use them to make the variable names more readable.

The answer to this question will appear in its proper place in Chapter 5.  However, we included the question here to let you know that it is indeed possible.