I once wrote a (very complicated) spreadsheet in Excel to calculate bonuses for drug peddlers at a pharmaceutical company. The problem screamed for a database, but the algorithm for calculating the bonuses was so complicated that it as a royal pain in the ass when I tried it. So I ended up with a fugly spreadsheet that still works 5 years on.

The ridiculous thing was that it could've all been well approximated with an exponential function, but that idea was a big no-no. The bonus algorithm is sacred.

In (mathematics) open-book exams I've taken, the books were essential. The highest scored solutions consisted of recognizing the problem, butchering equations for a few lines, and then pointing to the correct page in the correct book. The people who got highest grades were done in 15 minutes, though you were allowed to sit for at least 3 hours.

But, of course, to do that, you had to actually understand what it was all about, and you certainly couldn't learn that in 3 hours with all the books in the world.

That depends on where you live.