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Chemistry Level pending

What fraction of a radioactive substance will be decayed during 3 half lives?

1/8 1/4 1/3 7/8

1 solution

Shabarish Ch
Mar 3, 2014

Let $x$ be the amount of substance that was present initially.

After one half life, $\frac{x}{2}$ substance is remaining.

After two half lives, $\frac{x}{4}$ substance is remaining.

After three half lives, $\frac{x}{8}$ substance is remaining.

So, amount of substance that has decayed $1 - \frac{x}{8} = \frac{7x}{8}$