Section 6.7 Quiz 7.7 
Question: 
A radioactive substance decays exponentially, so the amount A left at time t is given by A = A_{0} e^{kt}, where k < 0. If there are 500 units of the substance initially and 149 units after 6 hours, what is the decay constant k (in hr^{1})? Express your answer to three decimal places and include the negative sign. 
