What grade is 42 marks out of 100 in a GCSE maths exam?

A score of 42 out of 100 on a GCSE Maths exam is a fail. While the exact grade boundary varies slightly from year to year and exam board to exam board, 42/100 is significantly below the pass mark which is usually around 60-70%. It would likely fall within a U or G grade depending on the specific grade boundaries.