State the rock was formed billions of years ago

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A rock contains 0.42 mg of Pb-206 and 0.53 mg of U-238. Approximately how many U-238 atoms were in the rock when it was formed billions of years ago? (The half life for 238U-->206Pb is 4.5x10^9 yr.

A. 1.3E18 atoms

B. 2.8E20 atoms

C. 1.1E18 atoms

D. 2.6E18 atoms

E. 1.1E17 atoms

Reference no: EM13175645

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