is an English television presenter and mathematician who currently co-presents the Channel 4 daytime puzzle show Countdown and its comedy spin-off 8 Out of 10 Cats Does Countdown.
A mathematics graduate, her television debut came when she joined Countdown at age 22.
In August 2016, it was announced that Riley would join Sky Sports to present Friday Night Football alongside her former Countdown co-presenter Jeff Stelling and Fantasy Football Club with Max Rushden and Paul Merson.
On 26 June 2009, it was reported that Riley had been recruited by Royal Mail to employ her mathematical skills to help advise holidaymakers on how to make the most of their holiday currency, after a report by the Post Office revealed that a significant number of holidaymakers fail to calculate the actual cost of goods and services when travelling abroad and often overspend their holiday budgets.
Her mathematics background and love of football has seen Riley assist bookmakers in preparing betting odds for football tournaments; based on her analysis she predicted Chile would win the 2014 FIFA World Cup, despite appreciating fans would see it as an unlikely outcome (Chile were ultimately knocked out in the Round of 16).
In October 2010, Riley presented a programme on the club's television channel, MUTV, featuring a tour of their Trafford Training Centre in Carrington.
Riley frequently encounters close media and public scrutiny of what she wears on the show, with her wardrobe choices attracting intense social media comment on Twitter and You Tube and even national headlines, particularly if they are deemed too revealing or tight.
In contrast, on account of her "really immature sense of humour" she has some difficulty in maintaining her composure during the words round whenever rude words appear.
Her co-presenters, Ben Miller and Romesh Ranganathan, similarly had a background in science and maths.
Explaining the purpose of the show as popularising science and making it seem less intimidating, she said "It's showing that you can't separate the world of science from the world we live in".
She added that while her background is in maths, "You can't separate them either.
Maths is the language of science." A key part of the show was a weekly challenge where one of the presenters "risked their lives" to prove a scientific theory – in Riley's case she cycled on a tightrope and zip-lined through a ring of fire.