Topic
Money
Counting coins, working out change, and figuring out whether the sale is actually a good deal.
The math you'll use most
Most adult math is money math: adding up totals, computing tax, working out a percentage off, comparing unit prices.
Counting money
Add up coins and bills.
Money & decimals
Cents are decimals of a dollar — every transaction is decimal arithmetic.
Make an amount
Build $1.37 with the fewest coins — a classic problem.
Wages & salary
Hourly, salaried, overtime — and how to compare offers fairly.
Percentages & discounts
20% off — what does that actually cost?
Interest
What interest is, why borrowers pay it, why savers earn it.
Simple interest
Interest on the original amount only — clean and predictable.
Compound interest
Interest earns interest. Slide the years and watch the curve bend up.
Compound interest derivation
Why A = P(1 + r/n)^(nt) — and where every letter comes from.
Budgeting
Income in, expenses out — build a balanced month.
Currency conversion
Convert between dollars, euros, pounds and more.
Investing basics
What a return is, what risk is, and why time helps.
Annuities
Regular payments — how to value a stream of cash flows.
Present value
What a future dollar is worth today — discount it back.
Net present value
Sum of discounted cash flows — positive means it's worth doing.
Internal rate of return
The discount rate that makes NPV zero — investing's headline number.
Insurance
Pool small premiums, pay big claims — risk-sharing as maths.
Rent or buy
When does owning beat renting? A comparison you can run with numbers.
Investment graph
Watch a starting balance grow under different rates — interactively.
What to do with money
Spend, save, invest, give — the big four moves with money.