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It is the contest Ultimate Fighting Championship (UFC) fans never knew they wanted.
On Sunday, Justin Bieber challenged Tom Cruise to join him in the octagon (the UFC ring) to solve a problem so fiendishly difficult no-one had previously bothered to think of it.
If a 25-year-old pop star stands 5ft 9in (175cm) and sells 150 million records, attracting 106 million Twitter followers, why does he randomly decide to try to goad a 56-year-old movie star into fighting him?
Needless to say, a calculation so onerous quickly won the attention of the very best minds the social media platform had to offer. Read more