Uranium-238 decays through alpha decay with a half-life of 4.46 10^9 years. How long would it take for 7/8 of a sample of uranium-238 to decay?

1. 8.92 10^9 years

2. 1.78 10^10 years

3. 4.46 10^9 years

4. 2.01 10^10 years

5. None of these

6. 6.69 10^9 years

7. 1.12 10^10 years

8. 2.23 10^9 years

9. 1.34 10^10 years

10. 1.56 10^10 years