App review by Debbie Gorrell, Common Sense Education | Updated October 2015
King Of 20
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King of 20

Misleading order of operations rules overshadow engaging game's appeal

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Subjects & Skills
Math, Critical Thinking

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Pros: A fun way to practice arithmetic, and kids are challenged to use critical-thinking skills.

Cons: One of the game rules violates a basic mathematical concept.

Bottom Line: Kids with knowledge of basic arithmetic will likely enjoy this game, but it's not recommended as a teaching or practice tool for the classroom.

The issue regarding the order of operations is reason to pause when using this game in the classroom. However, it could be used as a teachable moment. Have kids play one game and write down some of the longer expressions they create. Come together as a class and compare how the expressions were simplified according to the game rules versus how they should be simplified by following the order of operations. For example, simplifying the expression 8 Plus 2 Times 4 when following the game rules results in 40. Simplifying it correctly by following the order of operations results in 16.

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Kids start by choosing a beginner or advanced level for their opponent, which is the computer program. Then a tiled screen appears along with several number and operation tiles at the bottom of the screen. Kids are challenged to make an expression using the tiles with a solution as close to 20 as possible. They get points for anything greater than 20, and the lowest score wins. On each turn, kids place 1 to 3 tiles by dragging them onto the board, with the first expression of the game consisting of exactly 3 tiles. Kids can add tiles to an existing expression, but they are not allowed to create negative numbers and they're not supposed to follow the order of operations. Kids can pass or swap tiles if they cannot create an expression, but they incur penalty points. The game ends when the tiles run out, but players complete two rounds after this. Up to six games can be in progress at once.

While the game challenges kids to use arithmetic skills and critical thinking, it has a major flaw: The rules of the game instruct kids not to follow the order of operations. This may be fine for kids who have a solid grasp of arithmetic, but it could interfere with learning among less-advanced kids. As they play, kids can learn about strategies for writing numerical expressions that have a given value when simplified. They practice arithmetic skills and mental math as they form the expressions using numbered tiles and tiles that represent mathematical operations. For example, students may be given the numbered tiles 2, 3, 1, 6, and 8 and two tiles labeled "Plus." They can form the expression "8 Plus 6" to get as close to 20 as possible with the given tiles. On another turn, kids have the option to add tiles to this expression to get closer to 20. The game is a fun way to practice simplifying expressions, but as they create longer expressions with multiple mathematical operations, it's unfortunately misleading to have to keep track of actual math rules versus the rules of the game.

Overall Rating


Creating expressions to maximize gameplay advantage is addictive, but it can grow tedious to wait for the computer to take its turn.


Kids are challenged to use mental math and arithmetic, but the game violates a basic mathematical concept. With only two difficulty options, leveling is minimal.


There are clear, detailed instructions for playing the game. Extension ideas would be a welcome addition.

Common Sense reviewer
Debbie Gorrell Educator

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