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27 June, 17:04

A rock has 12.5 percent of its original amount of potassium-40 remaining in it; potassium-40 has a half-life of 1.25 billion years. How long ago was the rock formed?

A. 1.25 billion years ago

B. 2.5 billion years ago

C. 3.75 billion years ago

D. 5 billion years ago

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  1. 27 June, 17:24
    0
    If the rock has 12.5 % of its original amount of potassium-40 remaining in it, this has a half-life of 1.25 billion years, the rock was formed approximately 3.75 billion years ago. The correct answer is C.
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