Quote Originally Posted by pendell View Post
138 answers
6 answered 0
56 answered 1
2 answered 2
1 answered 3.5
4 answered 4
20 answered 5
3 answered 6
45 answered 7
1 answered 14

so ... 45/138 = 0.32 * 100 = 32% got the correct answer. If some kind person were to take a histogram , we should see a cluster around 5 and 7, another big spike around 1, and outliers everywhere else.

Does this imply that 68% of the population is so deficient in math skills that they do not understand primary school math? Well, the mean SAT score for mathematics is 501 out of a possible 800. This would imply (to me) that the average person is conversant with primary school math but at sea when it comes to secondary school mathematics.

So I conclude that the fault is with the writer of the equation. Yes, it may be technically clear and unambiguous. And if you're writing for an audience of mathematicians , that is probably good enough. But when only 1/3rd of your target audience is able to come to the correct answer, the logical conclusion is that either the person has failed to communicate clearly or that this is a deliberate trick question. Given the identity of the author, it is almost certainly the second.
Looking at this from an error analysis point of view:

56 (40%) probably used a calculator, badly
20 (14.5%) made the sign error (sign errors are very common)
45 (23.5%) got the correct answer
11 (8%) some random error, either hopeless or just messing around.
6 (4%) entered 0 (I'm not sure why here)

I think its quite an interesting maths question in that it exposes several common errors. Is it a trick question ? Or is it trying to teach something ?