Roger Webb

Excellent show.However occasionally the answers to the questions don appear to be correct.For instance Inrecently watched an episode where the question was how much of the earths surface is covered in water?the answer was 85%.I was always told at school it was 66%,however on checking this discrepancy all the information I could find was 71% of the earths surface is covered in water of which 91% is seawater. How do they research their questions and answers and are they checked for accuracy,if so by whom and how?