Context: The United Kingdom's constitution, being uncodified and largely unwritten, makes no mention of a prime minister. Though it had de facto existed for centuries, its first mention in official state documents did not occur until the first decade of the twentieth century. Accordingly, it is often said "not to exist", indeed there are several instances of parliament declaring this to be the case. The prime minister sits in the cabinet solely by virtue of occupying another office, either First Lord of the Treasury (office in commission), or more rarely Chancellor of the Exchequer (the last of whom was Balfour in 1905).

Question: When was prime minister first mentioned in a government document in the UK?
Answer: first decade of the twentieth century

Question: Who was the last prime minister to serve simultaneously as Chancellor of the Exchequer?
Answer: Balfour

Question: When did Balfour last hold the titles of prime minister and Chancellor of the Exchequer?
Answer: 1905

Question: Who's constitution is well codefied?
Answer: Unanswerable

Question: What office did not exist in any form in the UK until the early twentieth century?
Answer: Unanswerable

Question: Who was the forst prime minister to also be Chancellor of the Exchequer?
Answer: Unanswerable

Question: When did Balfour leave the offeice of Chancellor of the Exchequer to become Prime Minisater?
Answer: Unanswerable