of reinforcements per unit of time, usually per minute Heart rate, usually measured in beats per minute Economics/finance rates/ratios Exchange rate, how much one currency is worth in terms of the other Inflation rate, the ratio of the change in the general price level during a year to the starting price level Interest rate, the price a borrower pays for the use of the money they do not own (ratio of payment to amount borrowed) Price–earnings ratio, market price per share of stock divided by annual earnings per share Rate of return, the ratio of money gained or lost on an investment relative to the amount of money invested Tax rate, the tax amount divided by the taxable income Unemployment rate, the ratio of the number of people who are unemployed to the number in the labor force Wage rate, the amount paid for working a given amount of time (or doing a standard amount of accomplished work) (ratio of payment to time) Other rates Birth rate, and mortality rate, the number of births or deaths scaled to the size of that population, per unit of time Literacy rate, the proportion of the population over age fifteen that can read and write Sex ratio or gender ratio, the ratio of males to females in a population See also Derivative Gradient Hertz Slope References Measurement de:Rate