The majority of the Complaints Board at the ASA said the advertisement employed gendered stereotypes that were sexist and, as well as being offensive to women generally, the advertisement sent an unhelpful message to young women in particular.
The advertiser said it was an attempt at humour based on the idea that many people find maths difficult, regardless of their gender.
The Complaints Board said the ad was placed in female bathrooms and so the message was directed at women only.
The advertiser said: "It is never our intention to stereotype or denigrate the intelligence of women in our communications".
Although the advertisement had finished running when complaint was received, the complaint was still upheld.
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