The rule of 72 is an old banker’s rule of thumb to find out how long it will take to double your money at different interest rates. Financial literacy has become an increasingly important topic for K-12 education and we believe spreadsheets and headmath or mental estimation should be central to it. Rule of 72 combines both and gets students calculating compound interest. They can also see how expensive high credit card interest rates can be to them.
Author: Ryan McQuade
Peter’s Taxi
There are a wide variety of financial literacy problems. This is the kind of problem that appears on many tests. It does not ask you directly to find the cost of a taxi ride which includes both a fixed and variable amount. See if you can use this Lab to make this problem and problems like it easy for you to solve.
Place Value: Thousands
We extend the place value generator to 100’s of thousands to show you how the pattern of 1’s, 10’s, 100’s, continues to 1,000’s, 10,000’s, 100,000’s. Enter numbers and watch the expanded and compact forms of place value change. Pay special attention to using text units and take a look at the rule we used to add those units to the number while letting the number change.
Place Value: Decimals
We take our place value generator to decimals to help students see the simplicity of the place value pattern going right as well as left.
The Chessboard
We take that great old problem of the inventor of chess and the ruler of India and use it to see how powers of 2 grow in size. We start out with a chessboard and look at doubling each successive number. Then we seek a method of representing this doubling in a formula and introduce exponents and powers of 2. We ask you what kind of rule would you suggest that would keep your head and please the ruler?