- #1

- 4

- 0

**How many half lives have passed since a particular rock was formed if a sample of the rock contains 31 times as much lead-207 than uranium-235?**

**I know that I need to do a table and calculate**

**I know how to do this question but the thing I need help on is how do I know the number of atoms in order to do a table and calculate. Like I have the ratio of parents:daughter isotope which is 1:31 right? but how do I do this? Just tell me how and I will do it myself. Actually I don't know physics, I'm studying it all by myself and I got this question from my friend's homework and I'm stuck on it, there are 3 questions like it and I need help on how to turn this ratio into actual numbers in order to calculate how many half lives have passed. If I don't need to turn it into numbers then please tell me how do I solve this question? Thank you :)**

EDIT: okay so thats what I did is this correct?

1 - 31 half lives=5

2 - 30 half lives=4

4 - 28 half lives=3

8 - 24 half lives=2

16 - 16 half lives=1

32 - 0 half lives=0

so 5 half lives have passed

Correct??

Last edited: