Answer:
If 2 half-lives have passed, it means that the radioactive substance has decayed twice, so the number of remaining atoms would be:
1st half-life: 400,000 / 2 = 200,000 atoms remaining
2nd half-life: 200,000 / 2 = 100,000 atoms remaining
Therefore, after 2 half-lives have passed, 100,000 atoms would remain, rounded to the nearest whole number
Step-by-step explanation:
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