# Rate

A rate is a type of ratio that compares two quantities expressed in different units. There are many different types of rates that we encounter in everyday life.

Examples

- 3 pens cost $1.19. Items (pens) are one kind of unit and money ($1.19) is another.
- A jet may travel at the rate of 1,000 miles per hour. Distance (miles) is one kind of unit and time (hour) is another.
- The speed of light in space is 186,000 miles per second. Distance (miles) is one kind of unit and time (second) is another.
- The rate of interest on a loan for a new car was advertised as 5.9% per year. This is a more complex kind of rate. It compares a rate (percent, or parts per hundred) with another kind of unit, time (year).

## Rate per unit time

One of the most common type of rates you may encounter is some measure over a period of time. Below are some examples:

- Speed - how far you travel per hour on your bike
- Frequency - how many times your heart beats in a minute
- Volumetric flow rate - the volume of fluid that comes out of your tap per second
- Power - the amount of energy delivered to your residence per hour

## Rates related to economics/finance

Below are just a few of many finance related rates we have experience with at some point in our lives.

- Exchange rate - how much one currency, such as the US dollar is worth relative to another, like the Canadian dollar.
- Inflation rate - how much general prices change during the year relative to the beginning
- Interest rate - the price paid by someone borrowing money for use of the money

## Other mathematical concepts related to rate

Slope is a concept you may already have encountered. It describes the direction and steepness of a line. It is the ratio of vertical change to horizontal change of a line. Slope is also later used in calculus, where the slope of the line tangent to a curve is the derivative of the function at that point. The derivative is also referred to as the "instantaneous rate of change."