[Sorry about the misleading title, as the query isn't entirely about half-life, but I couldn't find any better way to condense my question to make a brief enough title anyways..... and]
Radioactive decay is [as far as I know] an example of a First Order reaction. If I'm not mistaken, half-life [represented by t1⁄2] is the time elapsed for a sample to reduce BY 50% of its initial concentration.
Extending this piece of logic further, a book I've read states that t3⁄4 would represent the time elapsed for a sample to reduce BY 3/4th or 75% of the initial concentration. They were also kind enough to provide the following relation between t1⁄2 and t3⁄4,
t3⁄4 = 1.5 x [t1⁄2]
But I'm a little uncomfortable with this relation. Because if you think about this intuitively, it would take one t1⁄2 to reduce a 100g sample [say] to 50g, subsequently it would require a second t1⁄2 to reduce the 50g sample [obtained previously] to 25g. So it took two t1⁄2 to reduce the 100g sample to 25g, in other words, it took two t1⁄2 to reduce the 100g sample BY 75%.
So shouldn't the relation be,
t3⁄4 = 2 x [t1⁄2]
So am I correct? If not, where have I erred?