HOW TO MASTER PERCENTAGES. Ask a journalist what percentage increase you get by going from 700 potatoes to 900, and more often than not you will be met with a blank stare. Many reporters studied the humanities when they were young and are not very confident with the basics of maths, even though those basics are crucial in many kinds of stories, starting with economics. If you struggle with numbers, you should arm yourself with an app like this. It will show you that moving from 700 to 900 potatoes means a 28.5 per cent increase, while going back down from 900 to 700 is a 22.2 per cent decrease. The app – which offers several other features – is very intuitive to use and is also free. Available for iOS.