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**A radioactive sample initially contains N atoms. After three half–lives the number of atoms that disintegrated is**

**A.7****?/8**

**B.3****N/8**

**C. 5****?/8**

**D. ****?/8**

**QUICK ANSWER…**

**A**

**DETAILS…**

**After first half-life, N/2 will remain.**

**After second half-life, N/2/2 = N/4 will remain**

**After third half-life, N/4/2 = N/8 will remain**

**If N/8 remains, the number of atoms that must have disintegrated = N – N/8**

**= 8N/8 – N/8 = (8N – N)/8 = 7N/8**

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

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

**KEY-POINTS**

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

**After each half-life, half of the preceding number of atoms will remain.****The number that must have decayed can be calculated by subtracting the remaining number of atoms from the original number.**

**You can freely add your own answers below or 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 2016 JAMB-UTME physics past question 32 /**

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