Rationale: Create a game that embeds the skills of adding and subtracting integers into a conceptual decision making structure.
Objective: Insert a set of integers into a 4-by-4 grid so that the sums of the rows and columns is a minimum.
All the students need is the game board and the list of sixteen numbers.
The board consists of sixteen boxes arranged in a four-by-four array. Space is left between the boxes to insert the addition and subtraction signs. You can give the students a blank board and have them all fill in the operations to match a board projected in the room, or you can write in the operations before you make photocopies. Every space between boxes needs to contain either an addition or subtraction sign.
The arrangement is somewhat arbitrary, but it helps to have a fairly even distribution of both signs to increase the chances of students having a variety of skills to practice. The goal of the game is to arrange the numbers so that the sum of every row and column is a minimum. If the board contains a large majority of subtraction signs, then a high frequency of positive numbers would allow the sum to reach lower levels. You can play with a pre-determined list of numbers you give to the students. You could allow them to choose between two lists, or generate the lists randomly on the spot using playing cards.
After all sixteen numbers are placed, students calculate the eight sums (four rows and four columns). The results of these eight are then summed to get their final result.
Lines of Reasoning:
Students usually play the first round of the game with a pseudo-random strategy. Some only look at the rows while making decisions (this is the most common in my experience) and others only look at the columns. Most begin with the foundation that to get the smallest sum, you need to add negatives and subtract positives.
It doesn't take long for students to realize that the boxes are more interconnected than originally evident. If we read the grid from left to right, the boxes on the right edge are more connected than the left edge. This means negative numbers fit naturally on the left edge. This seems like a great strategy, but there could be boxes on the board that are connected by two addition signs (one in a row and one in a column). It may be more profitable to use the negative numbers to negate both of those addition signs rather than placing it on the left edge.
Boxes connected with two negative signs seem like they should hold positive numbers, but if there are no positives available, perhaps the smallest negative number must due. Is it then more profitable to remove a negative number from the left edge and place it there to avoid adding the positive number twice? These are some of the decisions to be highlighted.
When final answers begin to percolate in, I like to ask, "What caused that arrangement to be lower?"
Contrasting arrangements on two boards is no simple task. If you want easy extensions, make the target the largest sum or the sum closest to zero. You can also only provide 15 numbers and allow them to insert a wild-card entry between -6 and 6.
Game Board Download:
You can alter the addition/subtraction ratio as you see fit. You can change their locations. The list of numbers in this sample game has been randomly generated randomly and there is nothing special about it. This download is a starting point; play with it to create subsequent rounds of the game.
Download a blank game board here.
Download the sample game here.
My students had some experience with integers, but remained tentative with their skills. This structure allowed them to think big-picture about the four possibilities of adding positives, adding negatives, subtracting positives, and subtracting negatives. I have a feeling that this structure may be overwhelming as an introduction.
Sunday, April 3, 2016
The testing of a task went horribly right.
Many people liked the number line better, but I decided to stick with the inequality signs because:
- Students see this type of two-bounded inequality notation with domain and range.
- The number line gave the impression of a single, fixed answer (because the fractions appear a definite, scaled distance away from each other).
I gave this question as a starter to a group of my grade nine students. They completed it in their portfolios.
Brief Summary of Action:
It is very hard to follow all student strategy without some type of documentation, but as far as I could tell, most of the student strategy followed two scaffolds.
- Start with the (open) middle
These groups began by focusing on the five digits necessary to fill in the equality in the middle of the prompt. Many centered their action around equivalent fractions to one-half. This actually prompted a shift in the reasoning to what was impossible rather than what was possible. One student noticed that if you chose one-half, you could not use two-fourths because the two had already been used. Another pointed out that this was doubly bad because none of the numbers were two digits. This triggered their group to create a list of other impossibilities. One-fifth proved to be particularly useless. Two-tenths, three-fifteenths, and five-twenty-fifths were all ruled out.
This action continued until the group settled on one of the possibilities. There was little debate about whether the choices made were correct, because almost every group acted as though multiple solutions were possible. (This is one of the strengths of the problem; it places students in an investigative stance). After the middle was chosen, the students created the two boundary fractions and compared sizes with common denominators or a variety of other estimation techniques.
- Set wide benchmarks
This subsection of the class was much smaller in size. They decided that the best way to ensure success was to create a really large fraction on the left and a really small fraction on the right. The problem would then be solved if the remaining five numbers could be written as an equivalent pair of fractions. These conversations were very fruitful as well. After hearing their strategy, I countered with the question, "How can you make a fraction as large as possible?"
The answers generally organized themselves around one of two possibilities: one-ninth and eight-halves or the reciprocal. Then the groups listed out the remaining middle digits and attempted to create an equivalent relationship (all the time confident that it would fall within the set range). If they couldn't find one, they swapped out a single digit, and re-doubled their efforts.
Probably the best conversation of the day came when I challenged the fact that one-ninth was the smallest possible fraction. (Even if there was a fraction with a double digit denominator).
New Problems Posed:
I knew this task was going to provide conversation, but many of those conversations also posed new problems. Nothing out of left-field, but great problems because they 1) were simple and elegant alterations and 2) required a serious re-evaluation of the original strategy.
Here are three:
Needless to say, what was planned as a ten minute opener to initiate classroom inter-action ballooned into a period long buzz of reasoning, argument, justification, and re-posing. That, for me, is a beta test gone horribly right.