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Senior math major Ben Campbell (Jim Sturgess) of Massachusetts Institute of Technology (MIT) is accepted into Harvard Medical School, but cannot afford the $300,000 fee. Despite a 44 MCAT score and top grades, Ben faces fierce competition for the prestigious Robinson Scholarship that would pay for medical school in its entirety. The director tells him that the scholarship would go to the student who "dazzles" him. Ben did not have anything to dazzle the director then, so he walks away, trying to write an essay with nothing in mind to compose it.
At MIT, professor Micky Rosa (Kevin Spacey) challenges Ben with the Monty Hall problem in one of his non-linear equation classes, which he solves successfully. Rosa looks at Fisher with a look of amusement and is impressed by Ben's non fluctuating decisions who clings onto his theories of 'variable change'. After looking at Ben's score on his latest non-linear equations paper, on which he got 97%, Rosa invites Ben to join his blackjack team, which consists of fellow students Choi, Fisher, Jill, and Kianna. Despite being told by Rosa that he had already gotten into the Harvard Medical School, Ben refuses to join the team on the premise he had been promoted at his job. Next day, Jill visits Ben at his job and attempts to coax him into joining the team. The system involves card counting, and the team is split into two groups. "Spotters" play the minimum bet and keep track of the count. They send secret signals to the "big players", who place large bets whenever the count at the table is favorable. Ben reluctantly joins the team, telling Rosa he is only doing so until he can pay for medical school.
Rosa takes the team to Las Vegas over many weekends; Ben comes to enjoy his luxurious lifestyle as a "big player" there. His performance impresses Jillâwho develops a mutual attraction with himâand Rosa. However, Fisher becomes jealous of Ben's blackjack success. Rosa kicks a drunken Fisher off the team after he insults Ben and incites a melee, requiring the team to scramble to cash in their stock of chips before the casino swaps out (a common practice after a fight). Meanwhile, security chief Cole Williams (Laurence Fishburne) monitors the blackjack team, having his eyes on Ben.
Ben, distracted by blackjack, does not complete his part of a project for an engineering competition, estranging him from his pre-blackjack friends. During the next trip to Vegas, an emotionally distracted Ben continues playing even after he is signaled to walk away, thereby losing $200,000 dollars. Angered and upset, Rosa leaves the team and demands that Ben repay him for the loss. Ben and his three remaining teammates agree to go into business for themselves; Williams, however, kidnaps Ben, beats him up, then lets him go after a dire warning.
Ben learns that he has been given an incomplete in one of his classes and, therefore, will not graduate, and that his winnings have been stolen from his dormitory room. He suspects that Rosa is behind the events but has no evidence. Ben reconciles with his friends and Jill, and approaches Rosa with an offer: he and the team will hit Vegas for one more attempt before the casinos install biometric software that will quickly identify card counters, as long as Rosa, once a very successful "big player", also plays.
Disguised, the team returns to Planet Hollywood and wins $640,000 before fleeing with their chips from Williams and his men. Ben and Rosa split up, with Rosa taking the bag of chips. Rosa escapes into a livery cab with the intention of stealing the winnings, but finds his bag is full of chocolate coins and that the casino manager is driving Rosa's cab.
It is revealed that Williams had made a deal with Ben after beating him up: he would let Ben come to Vegas for one night to make a lot of money gambling in exchange for Rosa. Rosa had won a seven-figure sum at Williams's casino by counting cards, a feat that cost Williams a pit boss job. After capturing Rosa, Williams confronts Ben and demands at gunpoint the bag of chips for his retirement; after giving up the money, Ben rejoins his friends and pre-blackjack friends, who have, in fact, been counting all night themselves. The film closes with Ben recounting the entire tale to a "dazzled" Harvard director.

Question: who invites Ben to join his blackjack team?
Answer: Rosa