Switch to using expr() function and make more interesting prpblem
Fix solution entry box and make better range of problems
Write function to simplyify terms in sum of expressions
Split into separate + and - exercises to make it easier to deal with hints
Rewrite rate problem hints
Change method of generating problem to avoid questions that simplify
Simplify fraction where required
Add solution
Remove unnecessary variables
Avoid the rare chance that the two constants could be 0 and the coefficients share a factor
Fix hint error
Add hint plural
Make numbers nicer
Fix formatting for money with negative values
Ensure prize in lottery is never negative
Add exercise with varibles in numerator
Add exercise with variable in the denominator
Fix solution for new problem
Start a rational expression object
Use correct stroke colours and remove redundant tag