In mathematics, a rate is the quotient of two quantities, often represented as a fraction. If the divisor in the rate is equal to one expressed as a single unit, and if it is assumed that this quantity can be changed systematically, then the dividend of the rate expresses the corresponding rate of change in the other (dependent) variable. In some cases, it may be regarded as a change to a value, which is caused by a change of a value in respect to another value. For example, acceleration is a change in velocity with respect to time.