Definition. Let y = f(t) be the distance travelled at time t. The average velocity travelled from t = a to t = b is defined by

The instantaneous velocity at time t = a is defined by

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Definition. Let y = A(t) be the quantity of a certain commodity at time t. The average rate of change of the commodity from t = a to t = b is defined by

The instantaneous rate of change of the commodity at time t = a is defined by

Discussion [Using Flash]