A half-life is the amount of time that it takes for a radioactive substance to decay to one half of its original quantity. Suppose radioactive decay causes 300 grams of a substance to decrease to `300 xx 2^(–3)` grams after 3 half-lives. Evaluate `300 xx 2^(–3)` to determine how many grams of the substance are left. Explain why the expression `300 xx 2^(–n)` can be used to find the amount of the substance that remains after n half-lives.