I ask them too because I teach alg, these problems become more complicated as the year moves on and they need to write their steps down because there are multiple steps. The ones that have been doing it in their heads for years suddenly cant seem to do that anymore and find themselves in a tricky situation because they don't know how to show their work.
At least three people have mentioned Gynzy to me in the last two weeks, and the site is a wealth of SMART Notebook resources for ELA, Math, Science, and Social Studies. Not exactly like the lame activities on PARCC--much better!