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Exam revision workbooks used by GCSE pupils taking Welsh exam board qualifications have been withdrawn after 90 mistakes were found in them.

A team from Cardiff University's School of Mathematics found about every three in 50 questions contained an inaccuracy, were misleading or supplied a wrong answer.

Publisher Hodder Education is now reprinting the edition and has asked for current copies to be destroyed.

´óÏó´«Ã½ research had led to the discovery.

The One Show commissioned Cardiff University to look at Mastering Mathematics for WJEC GCSE Practice Book: Higher alongside workbooks for five UK exam boards: WJEC, AQA, Pearson/Edexcel, SQA and OCR, some of which had officially endorsed the books.

Hodder Education apologised for the mistakes.

Group managing director Lis Tribe said: "We are human. We do our best. We have made a mistake.

"Where our process fell down, which is a real concern to me and to my team, is that there wasn't the final quality check that should have taken place. We simply missed a stage because of the pressure of getting the book out on time.

"We are actually very grateful to The One Show for bringing these errors to our attention and enabling us to withdraw the book and put them right."

A spokesman for the WJEC said: "We have worked with Hodder to produce endorsed material. However, we have not endorsed the revision guide in question.

"As it has not been subjected to our endorsement process, we are not responsible for its content and cannot comment on it.

"Of course, if we are made aware of any errors in non-endorsed publications, we make every effort to ensure that the relevant publisher is informed."

Dr Matthew Lettington, who oversaw the research, said the level of mistakes was "unacceptable" and some errors would have been "highly confusing" for students.

The WJEC practice book had the highest level of errors by a significant margin, with 90 mistakes out of 1,496 questions.

The others were:

The exam boards told the ´óÏó´«Ã½ final responsibility for fact checking lay with the publishers.

Pearson/Edexcel said it had already spotted and corrected the eight errors in its workbook and it was being recalled and destroyed.

Cambridge University Press and Oxford University Press both said all errors were looked into and corrected in the next reprint.

The One Show is broadcast on ´óÏó´«Ã½ One at 19:00 GMT.