Simple Interest

beginner22 min read

The simple-interest formula and its rearrangements, why simple interest grows the amount in an arithmetic progression, and the standard exam patterns: doubling and tripling times, and recovering the principal from two amounts at different times.

What you will be able to do

Apply the simple-interest formula and solve it for principal, rate or time.
Use the fact that simple interest per year is constant.
Find the time for a sum to double or triple at a given simple-interest rate.
Recover the principal and rate from amounts known at two different times.

What is inside this lesson

1What simple interest is
2The formula and its rearrangements
3Doubling and tripling
4Worked example: interest and amount
5Worked example: doubling and tripling times
6Worked example: principal from two amounts
7Common mistakes
8Quick revision
9Practice

The lesson itself is for members

Reading the 9 sections above, the worked examples and the practice set is free — the whole knowledge base is on the free plan, along with flashcards, private notes and Ask Onely.

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