You are dating Moon rocks based on their proportions of uranium-238 (half-life of about 4.5 billion years) and its ultimate decay product, lead.
Part A: Find the age for a rock for which you determine that 50% of the original uranium-238 remains, while the other 50% has decayed into lead. Express your answer using three significant figures.
Part B: Find the age for a rock for which you determine that 64% of the original uranium-238 remains, while the other 36% has decayed into lead. Express your answer using three significant figures.