# The half-life of bromine-74 is 25 min. How much of a 6.0 mg sample is still active after 75 min?

Jul 10, 2016

$0.75 \setminus m g$

#### Explanation:

Find the number of periods during which the disintegration of the radioiosotope took place.

 "number of periods " = ("time")/ ("half-life")

$\text{number of periods } = \frac{75 \setminus \min}{25 \setminus \min} = 3$

During each period, half the original amount disintegrates.

$6.0 \setminus m g \to \frac{6.0}{2} \to \frac{6.0}{4} \to \frac{6.0}{8} = 0.75 \setminus m g$

Note that each arrow represents 1 period.