In order to come up with an idea, it’s best to think about your hobbies, or any mathematical issue you’ve encountered before. A really common IA is for music, graphing sine curves for frequencies of different notes. My friend is a figure skater, so his IA was about speed necessary before beginning a jump. Most math IAs are heavily physics based. One IA I heard about was finding out the surface area of a coke can. So, try to think of anything in real life, a problem which you can then figure out using maths.