This is a useful and fun book, but don't assume you can complete these tasks just by reading. It takes significant practice to compute these problems in your head. So, if you are dedicated and willing to put in the time, it is worth the price and the effort. Though I will never be good enough to beat someone with a calculator, I am often able to work out problems in my head to the amazement of my friends and family. That alone is worth it. This was first Kindle purchase, and I am now hooked.