Goofs for
21 (2008) More at IMDbPro »

• Continuity: During the first meeting with Ben, the cards that Micky deals alternate from face up, face down, and missing altogether.
  
  
• Continuity: When Ben's mom is serving birthday cake to Ben and his friends, she serves Cam twice.
  
  
• Errors in geography: There are multiple errors in Vegas hotel locations - seeming to be in one hotel when the shot from the window makes it clear they are elsewhere, particularly when visiting a suite said to be at the Hard Rock but clearly the view is from a tall Strip hotel. The Hard Rock Hotel is neither.
  
  

• Errors in geography: In the montage scene showing the "extravagant" lifestyle of the group, the film cuts to scenes at the blackjack table, inside of clubs, etc. It's supposed to happen in or around the Planet Hollywood Casino/Hotel, but many of the locations shown are from Red Rock Casino game room and the club "Cherry". Red Rock is about 12.5 miles northwest of the Strip, surrounded by houses and deserts.
  
  
• Continuity: When Ben is handed his earnings from the first night a five dollar bill is seen on the outside of the bundle. Moments later a $100 is on the outside.
  
  
• Continuity: During the opening credits, while Ben is riding his bike on the road, you see the same orange PT cruiser go past twice and the same silver Chrysler 300C go past three times.
  
  
• Continuity: During the opening scene montage, when Ben is riding his bike across the bridge, the position of his backpack changes several times.
  
  
• Continuity: When Prof Rosa calls Cole, Terry answers the phone and places Rosa on hold. However, when Cole takes the phone from Terry, he does not take Rosa off of hold and proceeds to talk to him.
  
  
• Continuity: When Mickey and Ben are walking through the park before the first trip, there is no one behind them. The camera changes and there is a woman walking her dog and another man.
  
  
• Continuity: When Ben is riding his bike on the bridge, a young guy with a lady are passing in the back stage. After this, when a yellow stripped bus passed behind Ben, that young guy and lady disappeared (it seems, they jumped into water) then another lady in white jacket appears who was absent before in the back stage.
  
  
• Errors in geography: A scene in Boston shows Ben and Jill riding the red-line T inbound. She disembarks at a stop announced over the PA as "Quincy Center." That stop is outbound from the point they got on the T.
  
  
• Factual errors: There is no class 2.09 at MIT, though the 2.09 class seems to pay homage to 2.70 (aka 2.007) which is a renowned robotics competition.
  
  
• Plot holes: In two separate places in the film, the player is hollering for the dealer to draw a "monkey" (a face card or a ten) when, in fact, a monkey would have given the dealer a winning hand. The first instance is when an Asian woman introduces the main character to the slang. The more egregious of the two instances is when the main character (who, by this time in the film, has established his big player credentials) calls out for a monkey twice when either of those times would have given the dealer a winning hand.
  
  
• Revealing mistakes: During the opening credits, Ben is bicycling across the Mass. Ave bridge and cars and trucks are passing him at a good rate of speed, but his clothes and hair do not show any movement when there should be some resultant forward drag created by the aerodynamic drag from a passing vehicle.
  
  
• Continuity: The first night the group gambles in Las Vegas they are in the Hard Rock Casino, however the table at which Ben gambles says "Red Rock Casino". When he switches tables it says "Hard Rock Casino."
  
  
• Plot holes: If Ben didn't deposit his winnings in a bank to avoid suspicion or a paper trail, how was he planning on paying Harvard?
  
  
• Crew or equipment visible: When Ben leaves the Hard Rock Hotel after their first night in Vegas, the shadow of the Cameraman and Camera on the dolly are visible on the hotel front and security guards in the background.
  
  
• Factual errors: In the scene were we first see Ben in the casino playing for the first time, the count is +18. We then see a face card (worth 10) appear and Ben wins. Micky then asks him what the count is. He says +18, but it's really +17 because a face card has a value of -1.
  
  
• Revealing mistakes: All the cards in the casino scenes have rounded corners opposite the index numbers, identifying them as used cards that have since been removed from use on the casino floor and altered so they can never be sneaked back into play.
  
  
• Errors made by characters (possibly deliberate errors by the filmmakers): After Ben has the trial run, Micky and Ben are walking and Mickey says to him "Fisher and Jimmy have always been the big players, I want you to take Jimmy's place." Jimmy Fisher is one and the same person.
  
  
• Anachronisms: At one point the characters are enjoying an Amber Bock which was not available at the time the movie portrays.
  
  
• Continuity: During the chase seen at the end of the movie Kate Bosworth's character alternates between running in heels and running barefoot.
  
  
• Incorrectly regarded as goofs: "In the prize behind three doors game, the strategy of switching doors actually gives your overall odds to win of 50%, not 66%. Say the doors are A, B and C and the prize was behind B. There are four outcomes using the strategy: 1.You choose door A. Door C opens and you switch to door B, and win 2.You choose door C. Door A opens and you switch to door B, and win 3.You choose door B. Door A opens and you switch to door C, and lose 4.You choose door B. Door C opens and you switch to door A, and lose There are two scenarios that you win and two in which you lose. The probability of winning is 2/4 or 50%. Note that #4 is actually different than #3 and is disregarded by the movie, giving the 66% odds. Similar scenarios work if the prize was behind door A or C." This theory is actually incorrect. This scenario is referred to as the "Monty Hall Problem" and it's solution is a counterintuitive, making the problem a veridical paradox. Many explanations exist, but the easiest is this. If I initially chose door A for the car, I have a 1/3 chance of winning the car. The game show host, knowing the location of the car will open a door with a goat. Once a "goat door" is open, my original probability of 1/3 still exists, as I chose when 3 choices were present. Since the chance of the car being behind the opened "goat door" is zero, the remaining door has a 2/3 chance of having the car as the total probability of choices must equal 1, or 3/3. Therefore, you double your odds of getting the car by switching you choice.
  
  
• Factual errors: The price behind three doors game is actually wrong. The probability of winning the game once the "C" door has been opened is a plain 50%. The explanation is rather simple. The probability of choosing the right one from three doors (A, B, and C) provided it is NOT door C equals the probability of choosing the right one from two doors (A and B). You cannot take into account the probabilities of the earlier "game" (same way as we don't admit any probability to the car being behind door C once we see the goat it hid).
  
  
• Errors made by characters (possibly deliberate errors by the filmmakers): When Miles shows Ben the source code of the robot, Ben looks at them and immediately says this is very good. Actually, even a highly experienced programmer could not understand a source code just by looking at it for 2 seconds, especially the code of a really complex system such as this robot.
  
  

• Factual errors: SPOILER: A key clue that makes Cole Williams suspect Ben of being a card counter is that Ben did not double down on 11 when the count was "cool". Basic blackjack strategy dictates always doubling down on 11 (because the odds of getting blackjack are very high - even casual players know this). The only situation where it would make sense not to double down is if the count was very negative (lots of low cards in the deck). But as the "big player" in the MIT system, Ben would have left the table long before the count became negative.
  
  

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