Today, Uranium Contains $0.72 \%$ $235 \mathrm { U }$ (Half-Life = 0

question 35

Multiple Choice

Today, uranium contains $0.72 \%$ $235 \mathrm { U }$ (half-life = 0.70 billion years) and $99.28 \%$ ${ } ^ { 238 } \mathrm { U }$ (half-life = 4.5 billion years) . At a time 1.9 billion years ago, what was the fraction of $235 \mathrm { U }$ in uranium?

• A) 3.53%
• B) 4.72%
• C) 4.90%
• D) 6.76%

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