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**A substance has a half-life of 3min. After 6min, the count rate was observed to be 400. What was its count rate at zero time?**

**A. 1600**

**B. 1200**

**C. 200**

**D. 2400**

**QUICK ANSWER…**

**A**

**DETAILS…**

**3min = half-life,**

**6min = half of half-life = 400**

**If the half of half-life has a count rate of 400, it then follows that 3min earlier, the count rate was twice.**

**So, 3min = 400 ****×**** 2 = 800**

**0 min = 800 ****×**** 2 = 1600**

**Now for the right answer to the above question:**

**Option A is correct. 1600****Option B is incorrect.****C is incorrect.****D is not the correct answer.**

**KEY-POINTS…**

**You may please note these/this:**

**Simple understanding of what half-life is all about will help you trace the initial count rate.****Half-life simply means the time taken for half of a radioactive substance to decay.****Half-life for the substance above is 3min, after 6min, 400 counts remained, this implies that at 3min, 800 would have remained, and at the beginning, 1600 would have remained.**

**You are free to add your own answers below this page to assist others improve their learning.**

**You can also click the golden ASK A QUESTION BOTTON down this page to raise new related questions… OUR COMMUNITY OF EXPERTS WILL BE MORE THAN HAPPY TO TACKLE IT…**

**/ culled from 2020 JAMB-UTME physics past question 40 /**