Interest, loans and savings

Simple and compound interest, monthly loan payments and regular savings, with every answer checked a second way. About 10 minutes, GCSE / University.

What you will do

1. Money that grows. Interest is the price of using money. Simple interest is always a percentage of the original amount. Compound interest is paid on the original amount and on interest already earned.
2. Simple interest. Interest = principal × rate × time.
3. Compound interest. Multiply by (1 + r) once for each year: A = P(1 + r)^t.
4. A loan. A loan is repaid in equal monthly payments. Early payments are mostly interest; later ones mostly pay off what you borrowed.
5. Regular saving. Each deposit grows for as long as it stays in: the first for the longest. The sum of all of them is the future value.