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

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

Today, Uranium Contains 0.72%0.72 \%0.72% 235U (Half-Life =0.70= 0.70=0.70 Billion Years) And 99.28%238∪99.28 \% 238 \cup99.28%238∪

Today, Uranium Contains $0.72 \%$ 235U (Half-Life $= 0.70$ Billion Years) And $99.28 \% 238 \cup$