I decided to add all of the input of data on one screen and the results of the data on another screen. This helps to separate the two and focus in on the results. I added a SeekBar for the tips that is adjustable from 0% to 40%. I also have 3 buttons for 10%, 15%, and 20% tips. The neat thing is that clicking them not only changes the tip amount, but also adjusts the seek bar.
This is the first screen where you enter in all the data. There are buttons for the tip and also for choosing how many people to split it with.
This is the result page of the input data. It's not very fancy but it has everything you need, Bill Amount, Tip, Total Amount, and Split Amount.
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You can see all the functionality of the tip calculator in this video. Not much else to it.