# Introducing KenKen Puzzles

## Introducing KenKen puzzles

**Introduce KenKen(R) puzzles as a classroom cooperative puzzle.**

This page is for your background, to help you prepare. It is not a lesson plan or a prescription for teaching. You'll find your own style, but keep the focus on having the children puzzle things out.

**You have two very important roles as a teacher the first time you introduce these puzzles:**

- Your first task is mostly to be the "secretary," helping the children learn how to keep track of what they do know. You'll see examples of what this means below.
- You also have the job of teaching them the patience not to guess at what they don't know. Again, examples below.

Of course, you'll also have to help them learn the rules, and you'll want to model the "puzzling it out" process, but both of those can come as part of playing the first time, because it's hard to understand and remember all the rules before you start playing with the puzzles.

Puzzles are not just motivational play. A significant part of the Law School Admission Test is a kind of logic puzzle that sometimes appears in schools only as a rainy-afternoon diversion for students who have finished their "real" work! IQ tests and job-aptitude tests also frequently include puzzles that schools often treat as dessert. Puzzles are fun, but are extremely valuable ingredients in the "main diet," not just the dessert.

"KenKen" puzzles, also called "MathDoku" puzzles, exercise elementary school arithmetic -- addition, subtraction, multiplication, and division -- in ways that give excellent practice and also generate the thinking and problem-solving skills children will need for success in high stakes tests and later in algebra.

## Two good starter puzzles

Prepare: Download transparency to use in introducing KenKen.

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"Social solving"

Introduce the idea of solving the puzzle with another person, in a kind of turn-taking way. As you introduce the puzzles to the class, model the idea of looking around for a good place to start, or to go next, by scanning yourself for a place to go, and waiting a bit for student ideas. Do feel free to contribute ideas yourself -- after all, that's part of the turn-taking -- but not much, and keep to the simplest ideas, so that students have the chance to solve "harder" situations.

Some students may eventually prefer solving their own puzzles. Have a supply ready to play with.

## Rules for KenKen

It's hard to learn the rules all at once before interacting with the puzzle, so just the briefest introduction to the rules makes sense before diving in. Start with a 4x4 puzzle, like the one shown here.

- The only numbers you may write are 1, 2, 3, or 4. (A 6x6 puzzle requires 1 through 6.)
- No numbers may appear more than once in any row or column. (That is, all required numbers must appear in every row and column.)
- Each "cage" (region bounded by a heavy border) contains a "target number." If there's more than one cell in the cage, the target is also accompanied by an arithmetic operation. You must fill that cage with numbers that produce the target number, using only the specified arithmetic operation. Numbers may be repeated within a cage, if necessary, as long as they do not repeat within a single row or column.
- In a one-cell cage, just write the target number in that cell.

## Figuring out where to start

You can download this puzzle to project on a smartboard (or overhead projector) to introduce KenKen puzzles.

Special message #1: "Be lazy!" Look for the easiest place to start!

Students who are not used to solving puzzles may not know that there is no special order for working through puzzles like these, no "rule" for it. Finding the easiest places to start is part of what makes this a puzzle.

If a puzzle has single-cell regions, as this one does, they are obviously the "easiest" places to start. That number is the goal, no operation is needed, so we just write the number.

Now what?

Ask for ideas, but recognize that students are not yet likely to expect that solving a puzzle is about deduction not guessing. For example, they might guess that 3 and 1 could go in the first two cells of the first row. This fits the rules -- the goal is to make 2 using subtraction, and 3 - 1 = 2 -- but so would three other pairs of numbers: (2, 4), (4, 2), and (1, 3). We don't yet know which is correct.

As students make suggestions, you might fairly regularly ask "How did you figure that out?" Alternatively, if students make suggestions that are arithmetically correct -- like suggesting (3, 1) in those top left two cells because 3-1=2 -- you might also ask "do you know that those must be the numbers, or are you just saying that they might be?" This helps distinguish deduction from guessing.

## Modeling how to "puzzle" out a solution

After waiting long enough for students to have a chance, feel free to model "finding an easy place" by pointing to an "easy place" that you see. There are two good candidates in this puzzle.

Image:TeachingKenken4.png Image:12mmSpace.png Image:TeachingKenken7.png

We could start in either place.

Suppose we start with the "3,+" region. Ask students what might go in the two cells. (It must be filled with 1 and 2 -- no other pair of numbers adds up to 3.) When students give the numbers point out that we don't know which order to write the numbers.

Special message #2: "Be bold!" Even though we don't know everything, we do know something so we should write it down!

Special message #3: "Don't guess!" But, since we don't know what order they are in, we write them in a way that doesn't specify the order.

We know what numbers are there, so we can write.

Even this partial information is important. Pointing to the third cell in that row, ask students what they can now figure out about the number that goes in that cell. (We now know for sure that 3 goes there, because 1, 2, and 4 are already used up in that row.)

Alternatively, suppose we start with the "9,x" region. What three numbers can we multiply to make 9? Students may have had little experience with "products of three numbers," so this may not feel obvious. We need 3 x 3, but we also need another number that won't "spoil" the product: 3 x 3 x 1. Do we know where to write them? Well, the 3s can't both go in the same row or column, so.

What can we do next?

Now we might look at the "3,+" region. What can go there? (Just 1 and 2.) Do we know what order to write them? (Yes! The 1 can't go in the same column with the other 1.)

Now, what can we fill in? (Just by looking for what's missing, we can completely fill the first two columns and the second row.

And where might we go next? By this point, students may well have ideas about how to proceed.

## Puzzles on their own

After children really "know how," let them play on their own. Give "starter" (easy) KenKen puzzles to pairs of students. You might choose to give the same puzzle to each pair, or have a few different ones. The only purpose is to let them try on their own what the class just did together as a group.

These puzzles should be a regular feature of your classroom, so that students see that you consider puzzles "serious work" (even though they're fun!).

You might use them officially two or even three times a week. A small collection of starter puzzles -- easy 4x4 puzzles for beginners, and easy 6x6 puzzles for after that -- can be found below. After children are comfortable with these, more can be found on the web at the sites listed below.

Resources of KenKen(R) puzzles