Function to extract coeffcient for a given term
Basic solving rational expression exercise
Add answer and fraction simplification
Ensure variables don't cancel
Simplify code
Start improving hints
Add an exercise type showing equation not graph
Add method to evaluate an expression
Spell evaluate correctly
Improve hints
Add function to generate string showing how to evaluate
Improve hints to show how to evaluate each expression
More hints
fix plural in problem text, fix #47643

*isSingular(randRange( 1, 8 ))* and *<var>randRange( 1, 8 )</var> hour/s* are different numbers. i added a new variable *sleddingHours* and use it as *<var>sleddingHours</var> <var>plural("hour", sleddingHours)</var>*
avoiding rounding problem, fix #46111 and #49683

calculate with fraction like the hint instead of decimals.
39.9/12*60=199.49999999999997 is now 133/40*60=199.5
102.66666666666666/32*60=192.49999999999997 is now 77/24*60=192.5
fix wording in geometry_proofs_intro
Don't run MathJax on hints immediately

Summary: It's silly and slow to run MathJax on the hints which might not even been seen! Instead, move the MathJax-calling out to a separate module which (like graphie) is called when the content is actually presented. This should also be a bit faster in all cases because we only call MathJax once for the question area and once per hint instead of once for each `<code>` tag.

Test Plan:
reading_stem_and_leaf_plots.html feels faster; hints still appear correctly.
multiplying_expressions_0.5.html choices look the same; grading (including none of the above) works.
addition_1.html acceptable formats works.
graphing_linear_equations.html looks sane too.

Reviewers: eater, emily

Reviewed By: emily

CC: ben

Differential Revision: http://phabricator.khanacademy.org/D2967
Run tex better on multiple answer type, etc

Auditors: emily
Fix bad hints on solving_quadratics_by_factoring_2

Auditors: eater
removed unused variable AND_TEXT