## Flexi Says: The time required for half of the atoms in any given quantity of a radioactive substance to decay is the half-life of that element. To find out how much of a radioactive substance will remain after a given time, begin by determining the number of half-lives represented by the given time. Multiply 1/2 by itself for each half-life that passes in the given time. In other words, raise 1/2 to the power of the number of half-lives. For example, if the given time represents two half-lives, the amount remaining will be 1/2 x 1/2 = 1/4 of the original amount. If the given time represents 4 half-lives, the amount remaining will be 1/2 x 1/2 x 1/2 x 1/2 = 1/16 of the original amount.