Math challenges - Mathematical challenges for all

On the spirit of a mathematical homework for primary school pupils in Vietnam (1), we would like to introduce this game.
This game is very easy to play by putting suitable arithmetical operators into positions to obtain a right mathematical formula, but it is quite difficult to find solution for a given challenge.

Main features of this app are as follows:
- Give challenges with many difficult levels
(from very easy level for baby to quite difficult level for adult),
- Set level and time to play.

Have fun and enjoy!

References:

1. http://www.theguardian.com/science/alexs-adventures-in-numberland/2015/may/20/can-you-do-the-maths-puzzle-for-vietnamese-eight-year-olds-that-has-stumped-parents-and-teachers