The app choses a random number within a giving range, you are then to enter your guess of the number in as less trials as you possibly can.
the easy level requires at most 8 optimum trials.
the medium level requires at most 11 optimum trials.
the hard level requires at most 14 optimum trials.
The secret to winning is that with each guess,you should be able to eliminate half of the Numbers, then half of the numbers, and so on, until you zero in on the target Number.