Question

A city's water supply is contaminated with a toxin at a concentration of 0.63 mg/L. For the water to be safe for drinking, the concentration of this toxin must be below 1.5 x 10-3 mg/L.

Fortunately, this toxin decomposes to a safe mixture of products by first-order kinetics with a rate constant of 0.27 day–1. How long will it take for the water to be safe to drink? 0:30am (thats the rest of the question!)