This app is helpful IF you know how to use it. I got very frustrated with it at first because it kept telling me I was incorrect when I knew I was right. The trick is to not use the 1's in the equation. I don't know why they offer it (because you can't be correct if you use it) so don't use them when balancing, it will tell you that you're wrong, instead, don't put a number in and it will mark you correct.