Question

The radioactive substance strontium-90 has a half-life of 28 years. In other words, it takes 28 years for half of a given quantity of strontium-90 to decay to a non-radioactive substance. The amount of radioactive strontium-90 still present after t years is modeled by the expression 80*2^t/28 grams. Evaluate the expression for t = 0, t = 28 and t = 56. What does each value of the expression represent?

Answer 1

80 * 2^0 = 80*1 = 80g (amount initially) 
80 * 1/2 = 40 g (amount remaining after one half life) 
80* (1/2)^2 = 80* 1/4 = 20 g (amount remaining after 2 half lives).