I have my Math test coming up. I got 2 chapters that I need to prepare for. 1. Direct and Indirect Proportion/Variations
2. Indices and Standard Form

My school uses Oxford's New Syllabus Mathematics 7th Edition Book 2 and Book 3.

Can someone explain me these topics briefly? Tell each topic's formula and what it is and why it is what it is. I'll really appreciate if you take your precious time out. If I had any further queries on your answer I'll ask through comments, hope you'll reply. Thank you! ​