[yummyfajitas]

I don't understand how math answers without workings presented and marked are in any way useful or anywhere near "the right track"?

The goal is to have a score which is a) standardized and objective b) well correlated with mathematical knowledge in the curriculum.

Bsilvereagle identified a flaw with my particular example - students can substitute an easier problem for the real problem. But there are mechanisms to fix that. So given fixes for particular flawed questions like that, it seems like a typical standardized test will provide both (a) and (b).

It would be quite a coincidence if a student could write down the answer to many questions without knowing the intermediate steps, no? (I'm of course assuming security is sufficiently strong, i.e. no cheating.)