# Counting Cards – II

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Since we have introduced the game of blackjack at the end of last year, we can now talk about the winning strategies. A hand with an ace valued as 11 is called “soft”, meaning that the hand will not bust by taking an additional card; the value of the ace will become one to prevent the hand from exceeding 21. Otherwise, the hand is “hard”.  Each blackjack game has a basic strategy, which is playing a hand of any total value against any dealer’s up-card, which loses the least money to the house in the long term. For example:

For details, like when to double-hard or double-soft, see: https://www.blackjackarmy.com/basic-blackjack-strategy

Blackjack’s house edge is usually between 0.5%–1% when players use basic strategy. Card counting can give the player an edge of up to 2% over the house.

A card counting system assigns a point score to each rank of a card. When a card is exposed, a counter adds the score of that card to a running total, the ‘count’. A card counter uses this count to make betting and playing decisions according to a table which they have learned. The count starts at 0 for a freshly shuffled deck for “balanced” counting systems. Unbalanced counts are often started at a value which depends on the number of decks used in the game.

The most common variations of card counting in blackjack are based on statistical evidence that high cards (especially aces and 10s) benefit the player more than the dealer, while the low cards, (3s, 4s, 6s, and especially 5s) help the dealer while hurting the player.

Basic card counting assigns a positive, negative, or zero value to each card value available. When a card of that value is dealt, the count is adjusted by that card’s counting value. Low cards increase the count as they increase the percentage of high cards in the remaining set of cards, while high cards decrease it for the opposite reason. For instance, the Hi-Lo system subtracts one for each dealt 10, Jack, Queen, King or Ace, and adds one for any value 2-6. Values 7-9 are assigned a value of zero and therefore do not affect the count. Here is a quick explanation of this system:

A lot of content for this post was shamelessly copied from other articles. In case of copyright violation, please ask me to delete this.

# Counting Cards – I

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You would have seen the bad consequences of “counting cards” in blackjack game in casinos in movies like Rain Man and 21. This method allows the player to play a perfect game so that the odds are in the player’s favour to win.

In this post, let’s first understand what is blackjack. Most parts have been shamelessly copied from http://www.bicyclecards.com/how-to-play/blackjack/ . You can consider this post to be a tl;dr. If not happy, consider SMMRY.

In the casino version, the house is the dealer. The dealer remains standing and the players are seated. The dealer is in charge of running all aspects of the game, from shuffling and dealing the cards to handling all bets. Between one and eight standard 52-card decks are shuffled together and the cards are dealt from a shoe (a box that allows the dealer to remove cards one at a time, face down, without actually holding one or more packs).  Each card has some value assigned to it. It is up to each individual player if an ace is worth 1 or 11. Face cards are 10 and any other card is its pip value.   A hand’s value is the sum of the card values. Each participant attempts to beat the dealer by getting a count as close to 21 as possible, without going over 21.

When all the players have placed their bets, the dealer gives one card face up to each player in rotation clockwise, and then one card face up to himself. Another round of cards is then dealt face up to each player, but the dealer takes his second card face down. Thus, each player except the dealer receives two cards face up, and the dealer receives one card face up and one card face down. If a player’s first two cards are an ace and a “ten-card” (a picture card or 10), giving him a count of 21 in two cards, this is a natural or “blackjack.”  If the dealer’s face-up card is a ten-card or an ace, he/she looks at his face-down card to see if the two cards make a natural. If the face-up card is not a ten-card or an ace, he/she does not look at the face-down card until it is the dealer’s turn to play.

The player to the left of the dealer goes first and must decide whether to “stand” (not ask for another card) or “hit” (ask for another card in an attempt to get closer to a count of 21, or even hit 21 exactly). Thus, a player may stand on the two cards originally dealt him, or he/she may ask the dealer for additional cards, one at a time until he/she either decides to stand on the total (if it is 21 or under) or goes “bust” (if it is over 21).  The dealer then turns to the next player to his left and serves him in the same manner.

When the dealer has served every player, his face-down card is turned up. If the total is 17 or more, he/she must stand. If the total is 16 or under, he/she must take a card. He/she must continue to take cards until the total is 17 or more, at which point the dealer must stand. If the dealer has an ace, and counting it as 11 would bring his total to 17 or more (but not over 21), he/she must count the ace as 11 and stand.

There are three special moves called splitting pairs, doubling down and insurance.

• Splitting pairs is possible if a player’s first two cards are of the same denomination, such as two jacks or two sixes. The player may choose to treat them as two separate hands when his/her turn comes around. The amount of his/her original bet then goes on one of the cards, and an equal amount must be placed as a bet on the other card.
• Doubling down is possible when the original two cards dealt total 9, 10, or 11. When the player’s turn comes, he/she places a bet equal to the original bet, i.e. doubling his/her bet, and the dealer gives him/her just one card, which is placed face down and is not turned up until the bets are settled at the end of the hand.
• Insurance is possible when the dealer’s face-up card is an ace.  Any of the players may make a side bet of up to half the original bet that the dealer’s face-down card is a ten-card, and thus a blackjack for the house.  Insurance is invariably not a good proposition for the player unless he/she is quite sure that there are an unusually high number of ten-cards still left undealt.

# Puzzle : Free cab ride

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Today, intra-city cab services are provided with aid of mobile apps. So to promote usage of their apps they have following condition and offer:

If you install the app, you need to register your app with your mobile number and you can’t register with your mobile number more than once. You suggest the app to others and those people who use your reference code in registration, get a free ride. Once the people using your reference code avail their first free ride, you get a complementary free ride (corresponding to each person). So, every time a person avail a free ride using your reference code, you get a free ride!

Now my problem for you is:

There are $n$ people (each having only one mobile number) acquainted to each other and want to exploit this offer of free rides. What is the maximum number of free rides this group of $n$ people can enjoy?

You can post you solution in comments, I will post my solution later. Happy puzzling.