How to develop applications for training mental counting correctly and on what basis?

Question

Mobile development

With friends, we decided to write an application for Android, if successful, write it for IOS. The essence of the application is that the player / user is invited to add / subtract / multiply / divide two numbers orally and write the answer in the field. To make it easier for us, we searched for applications of similar topics, found this application:

We started writing it on the Android SDK, but we decided to make sure that this environment is suitable for a specific craft (so far only for android). Maybe there are also multi-form development environments, right away for IOS? Found cocos2d, haven't tried it yet. Waiting for your suggestions, maybe advice; what environment to choose, you can offer your options, only there is one condition: that documentation or forums can be found.

Answer 1

AIR flash.
But since there is not much code in such an application, it is better to make both versions in the native environment.
Pros in application size.
If you need help porting to AIR I can help

Answer 2

Write in HTML5+JS. The application does not seem to be complicated.
Here is an interesting framework ionicframework.com