Hacking high school exams and foiling them with statistics

Blogspam, go here for the original.

http://deedy.quora.com/Hacking-into-the-Indian-Education-Sys...

That has all the real graphs. They make it really obvious that the test must not be scored on a continuous spectrum, but is chunked into increments of more than one point. But there are also some curious bimodal effects that could indicate tampering at significant levels like 90%.

Doesn't the pattern depend on the value of each question? For example, if you have a score out of 100, but all questions are worth 4 marks, then you'd end up with a series of grades that are multiples of 4 (assuming no part marks).