"Guess My Rule" came from the Rodel Foundation. To play I put a secret algebraic rule (expression) under the Guess My Rule machine. Then we put a number into the machine and see what comes out. We record our input and output on a chart. Students then get to guess the rule. If someone writes a rule that you agree with, you can put a check mark next to the rule.
In this example, we put in a 1 and got a 3. So our rule could be "divide the input by 1, then add 2" because 1 divided by 1 plus 2 equals 3. Or our rule could be "add 2" since 1 plus 2 is 3.
Then we put another number into the machine. We check our first guesses. If they don't work for both sets of input/output numbers, we erase them and guess again.
When we put in a 2, we got an 8. That means that our first guess of "divide by 1, add 2" doesn't work because 2 divided by 1 plus 2 equals 4, not 8. Our second guess doesn't work either because 2 plus 2 is 4. So we erased both guesses and guessed again.
We continue putting numbers into the machine until we find a rule that works for all our inputs and outputs.
In this example, our guess of "multiply by 5, subtract 2" works for all three number pairs.
Finally we check our rule by moving the machine to see the rule underneath!
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