A sample has 320 radioactive nuclei. How many remain undecayed after 4 half-lives?

Answer and explanation

Correct answer: A. 20 nuclei

  1. Step 1: After half-lives . Answer: 20 nuclei. Why not the others: 80 nuclei: divides by the number of half-lives instead of . 40 nuclei: divides by twice the number of half-lives. 10 nuclei: uses one half-life too many.

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