Q. 1395.0( 1 Vote )

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 × 2–3 grams after 3 half-lives. Evaluate 300 × 2–3 to determine how many grams of the substance are left.

Explain why the expression 300 × 2–n can be used to find the amount of the substance that remains after n half-lives.

Answer :

Given, 300 grams of a substance decrease to 300 × 2-3 after 3 half-lives.


Evaluating 300 × 2-3


We know by laws of exponents, a-n =


300 × 2-3 = = = = 37.5 grams


3.75 grams of the substance are left.


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