Master Simple Interest, Compound Interest & Smart Financial Decisions | Financial Matters Explained

In this in-depth financial mathematics tutorial, we break down the core concepts of simple interest, basic interest, and especially compound interest—the key to understanding how your money really grows (or how much debt actually costs). Whether you’re a student, investor, borrower, or just want to make smarter money moves, this video gives you the practical tools you need. We start by clearly illustrating the simple interest formula: I = P × r × t (or sometimes written as I = Prt) You’ll learn exactly what each variable means: • I → Interest earned or paid • P (or Capital) → Principal (the starting amount of money) • r (lowercase r) → Annual interest rate in decimal form • t → Time in years We then move into the powerful compound interest formula (often remembered as PARNNT): A = P(1 + r/n)^(nt) You’ll learn exactly what each variable means: • A → Final amount (future value) • P → Starting principal (initial investment or loan amount) • r → Annual interest rate in decimal form • n → Number of compounding periods per year • t → Time in years We also clearly explain APR (Annual Percentage Rate) and why the “A” in APR stands for annual—and how it affects real-world loans, savings accounts, and investments. We then rearrange the compound interest formula to easily calculate the interest paid (Interest = A − P) so you can see the true cost of any financial product at a glance. A big focus of the video is the powerful blend of old-school analytical methods (handwritten calculations the instructor refers to as “old school” techniques) with modern technology. We demonstrate traditional step-by-step solving by hand, while also using Desmos — the free, beautiful graphing/scientific calculator — as an inexpensive visual tool. This includes graphing linear equations and using vertical lines to find intersections as an intuitive way to solve certain simple interest problems visually. We also show how to use Desmos to assign variables, so you can simply plug in the form

Added 11 Apr 2026