Question

The half-life of oxygen-15 is 124 s. If a sample of oxygen-15 has an activity of 6400 Bq, how many minutes will elapse before it has an activity of 400 Bq?

Answer 1

8.27 minutes

Step-by-step explanation:

Do the half lives first. 6400 Bq->3200 Bq->1600 Bq->800 Bq->400 Bq

The arrows represent one half life therefore there are 4. Next you multiply the 124 second with the 4 half lives. You get 496 second so you would divide that by 60 seconds which will give you 8.27 minutes.