I've been a member of Swagbucks for a bit, and I've earned over $300 in Amazon.com gift cards since then. Amazon.com gift cards are one of the best deals that Swagbucks has going on, and they're almost as good as cash, since you can get just about anything on Amazon.
I recently signed up to tutor someone in business math. The mechanics of getting to the correct answers is well within reach for me, but the terminology was something I didn't have at my fingertips. And, hopefully after rubbing elbows with personal finance nuts as long as I have, I could pick it up quickly enough to stay ahead of her.
At roughly the same time, my mother-in-law was taking a similar short course. Her textbook for the course was the Basic Business Mathematics Schaum's outline. These threw me back to my college and grad school days; I had collected about a dozen of them.
These are great for getting up to speed in a subject. Each has concise material, worked-out example questions, and supplementary questions. They're also cheap. The list price is only $19. It's far cheaper than a big textbook, and nearly as good.
A used version was available through Amazon for about $2.03 (plus the standard $3.99 flat rate shipping).
But after applying one of the $5 Amazon gift cards I earned from Swagbucks, it was a whopping $1.02, shipped to my door. Even better, since the seller was in a neighboring state, I got it in four days.