Merge branch 'sim-rat-exp' of https://github.com/petercollingridge/khan-exercises into petercollingridge-sim-rat-exp
Redo rational expression module
Merge remote-tracking branch 'upstream/master'
Add exercises to plurals
Use plural exercises in arith word problems
Make hints more consistent
Merge pull request #45051 from petercollingridge/push-ups

Add exercises to plurals