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1. we start with 400 atoms of uranium-238. how many remain after 4.5 billion years? after 9 billion years? after 13.5 billion years?

2 . how long will it take for ½ of the original amount of rubidium-87 to decay?

3. carbon-14 has a half-life of 5,730 years. how does that compare to those listed in the chart?

what possible advantages or disadvantages would this give c-14 when used for radiometric dating?