Fix verb tense

Auditors: eater
Don't talk about the answer format in the question

Auditors: eater
Algebraic property wording tweaks

Auditors: eater
Merge branch 'i18n' of github.com:Khan/khan-exercises
Revert pluralization function until new version is landed.
Merge branch 'master' of github.com:Khan/khan-exercises
Resolve merge conflict.