Helen Ball is co-author of the new Collins Core Maths resources. She is an ex-IT project manager who switched to maths teaching, rising to Head of Mathematics and teaching from KS3 through to KS5. She is an IGCSE and A-level examiner.Chris has an MA in Maths and over 30 years' teaching experience at secondary level, including a local advisory role. He is the author of our endorsed edition of Cambridge IGCSE Maths Student Book and has written and co-authored numerous Collins maths publications at this level. He also has written for Cambridge Checkpoint.