What ihe basis for the determination of Uranium 238-Lead radiometric date of 1120 ma for granite

Question

Wouldn't it be the ratio of U238 and lead in the granite?

I do not think so, i have actually answer the question explaing it in words but i am not sure of it as the question is confussing

I take it this is S103 TMA08 Q2(b) (10 marks) "The age of a granite can be determined using radiometric dating. Explain the basis for the determination of a 238U-Pb radiometric date of 1120 Ma for a granite."

The key word here is "explain". There is nothing to calculate.

The best source of information is the course books.