Original Card Games by David Parlett
Players 2   Cards 52   Type Arithmetical
I like arithmetical games. What more is there to say?

Preliminaries
The turn to deal alternates. Deal six cards each from a 52-card pack. Turn the next (13th) card to start an adding-up pile and announce its face value as the first count. For this purpose Queen = zero, Ace = one, and numerals Two to Ten count 2 to 10 respectively. If the turn-up is a Jack or King the initial count is zero.
Object
To play in such a way that the total made by playing your sixth and last card is as close as possible to that of the card itself - for example, by bringing the total to 9 by playing a 9 last. For this purpose a Jack or King played last counts zero.
Play
Each in turn, starting with the non-dealer, plays a card and announces a new current total as follows:
• If the card you play is higher than the previous count, add it to the count.
• If it's lower, divide it into the count if it divides without remainder, otherwise subtract it.
• If it's equal, you may add, divide or subtract it.
• A King halves the count if it is even, otherwise doubles it.
• A Jack counts exactly the same value as the card it follows, or acts like a King if it follows one.
Note: You may not divide by zero (a Queen), otherwise the world will come to an end.
Score
When you have both played your sixth and last card you each in turn announce the difference between its value and the count you made with it. Your opponent will score the square of this number. For example, if Adam's sixth card is a 2 and brings the count to 6, Eve will score 16 (the square of 6 minus 2); and if Eve then plays a 3 and brings it to 3, Adam scores 0.
Bonuses and penalties
There are certain 10-point bonus and penalty plays. When you score a bonus, mark it by drawing a card from those not in use and placing it face down in front of you.
• If you play a card of the same rank as the previous card, you get a bonus.
• If you play a card of the same suit as the previous card, your opponent gets a bonus.
• If your last played card is exactly equal to the total it makes, you get a bonus.
Game
Keep a running total and play up to any agreed target, such as 101 for a short game.
Optional extra
You may multiply the current total by the card you play provided the product is not greater than 20.