For the radioactive isotope and associated half-live (assume that decays according to the formula A(t) = A0ekt where A0 is the initial amount of the material and k is the decay constant):

Find the decay constant k. Round your answer to four decimal places.

Find a function which gives the amount of isotope A which remains after time t. (Keep the units of A and t the same as the given data.)

Determine how long it takes for 90% of the material to decay. Round your answer to two decimal places. (HINT: If 90% of the material decays, how much is left?)

Cobalt 60, used in food irradiation, initial amount 50 grams, half-life of 5.27 years.

**Subject Mathematics Algebra**