# Year 9

## Number and Algebra

### Simple interest

Long before decimals were used, the need to work with tenths, twentieths and hundredths was evident. Roman taxes were calculated on the basis of these types of fractions. For example, Emperor Augustus (63 BCE – 19 CE) levied a tax of 1% on goods sold at auction and a tax of 4% on every slave sold. The Romans did not use this notation but certainly employed the concept that we use today.
The concept of percentages has been used since ancient times, but the use of the % sign is quite recent and its exact history is uncertain.
Interest on money borrowed is an ancient practice.  Banks and other money lenders publish the rate at which interest is charged as a percentage and the borrower makes the payment. Conversely, if a person invests in a bank or another lending institution, then the bank pays the person interest on their investment because the bank uses the money to finance its own investments.
In simple interest transactions, the interest is charged only on the original amount borrowed.