Wolfram Alpha- This is a great app whenever you are stumped on how to work out a problem. It is available in the app store and costs $1.99. You can also visit the Wolfram Alpha website. This site is amazing in the fact that you can type in a problem and it will walk you through the process of solving and give you multiple formats for your answer.
Fractions by McGraw-Hill: This is a FREE app that is a game to help review equivalent fractions. It is more of a game but is VERY beneficial.
Math Skills- Another FREE app that goes over basic Math Skills. You can choose different levels with all four operations. This is a great refresher and mind bender!
Logic Factors Lite- Another FREE app that will test your logic! You have 16 different levels in the Lite version that are all very mind-bending.