Use the Fact That the Quantity of a Radioactive Substance

Multiple Choice

Use the fact that the quantity of a radioactive substance after t years is given by where is the original amount of radioactive material and k is its half-life (the number of years it takes for half the radioactive substance to decay) . The half-life of strontium-90 is 25 years. Find the amount of strontium-90 remaining after 9 years if Round your answer to one decimal place.

A) 13.6 kg
B) 72.5 kg
C) 7.5 kg
D) 119.4 kg
E) 0.2 kg