Hi guys, it is an application for children who want to practice their math by themselves or with friends. Also teacher can create math groups for their students. I designed it 2 years ago. 
Here is the prototype link: 
https://invis.io/AHS1LNSJK3S

And app store link: 
https://itunes.apple.com/vn/app/matevo/id1321846265?mt=8

All the best. Thank you.