Scientists estimate Earth's age to be 4.6 billion years. Samarium has a half-life of approximately 106 billion years. From the present date, approximately how many more years must pass before a sample of samarium that was created at the beginning of Earth's history contains 25 percent of the original parent material?

10 billion

26 billion

100 billion

206 billion

Question

Scientists estimate Earth's age to be 4.6 billion years. Samarium has a half-life of approximately 106 billion years. From the present date, approximately how many more years must pass before a sample of samarium that was created at the beginning of Earth's history contains 25 percent of the original parent material? 

 10 billion 

 26 billion 

 100 billion 

 206 billion

blues · Answer

This is a math question about exponential decay. You would get better help if you posted it in the math group. http://openstudy.com/study#/groups/Mathematics