:5 Uranium-238 (U-238) has a half-life of 4.5 billion years. Geologists find a rock containing a mixture of U-238 and lead, and determine that 55% of the original U-238 remains; the other 45% has decayed into lead. How old is the rock? 1/1 :5 file: . .. 5/1 1:5 The rock is billion years old. (Round to three decimal places as needed.) 6/1 1:5 6/1 1:5 6/1 1:5