The release of chlorofluorocarbons utlized in air conditioning and household sprays destroys ozone in upper atmosphere. At present time, amount of ozone, Q is decaying exponentially at the continuous rate of 0.25% per year. Find half life of ozone? Or we can say, at this rate, how long will it take for half ozone to disappear? If Q0 is initial quantity of ozone, then Q=Q0e-0.0025t, then determine t.