Using the following data to complete the problems below:

Dating System. Age of half life
238 U->206 Pb 4.5 billion years
235 U -> 207Pb 713 million years
40k-> 40Ar 1.3 billion years
14C-> 14N. 5,730 years

A rock originally has 2200 atoms of 235U and no 207 Pb. It now has 800 atoms of
235U. Assuming the only chemical process is the radioactive decay of uranium to
lead, what is the age of the rock?
a) 1745 million years
b) 1040 million years
c) 2643 million years
d) 2032 million years
e) 713 million years

How many atoms of 207 Pb are there in the rock now?