'Technical' fixes for 'Contest Week 2', fix #185, #186, #187.
Fix formulas, numbers and some typography in several articles

Also I made some little text fixes, where I see mistakes; add some tex
examples to 'make whatif' page and enable formulas for 'page' type
pages; fix dollar sigh rule from "30 $" to "$30" and made appropriate
changes in articles.

Fix #441, #442, #443, #406.