improve formatting by removing backslash.
Use custom answer checker to allow multiple correct answers
New lin alg problems.
Minor fix.
New linear algebra problem.
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
correct domain for log checking.
New optimization problem.
Small fix.
Add clarifying instructions to problem text

(in millions of barrels per day)
Small fix.
Merge branch 'master' of git://github.com/openwebwork/webwork-open-problem-library
Add "no real solutions" to problem text.
Add "no real solutions" to problem text.
Add "no real solutions" to problem text.
Add "no real solutions" to problem text.
Add "no real solutions" to problem text.
Add "no real solutions" to problem text.
Add "no real solutions" to problem text.
Making display a little better.