Mystery Op 4
(page 39)

The following solution is from Mrs. Hersh's 8th grade FOCUS - Problem Solving Class at Crabapple Middle School, Roswell, Georgia (different group from the one that did Mystery Op 3, specifically from Tivina Johnson, Zain Husein, Jessie Hillegas and Ayumi Hara )

We called the operation symbol "Left Point Isosceles Triangle" (use Left Point for short:))

Take the first number (in front of Left Point) and subtract 1

Take the second number (on other side of Left Point) and add 1

Then multiply the two numbers, and the product equals the answer on the other side of the equals sign.

Hope this is correct! Hopefully my next group will get Mystery Operation 5!!!

We look forward to hearing from you!

eeps responds:

Thank you for your lovely submission. I wonder what made you think of that solution? How did you decide what the operation must be?

Also, since you're eighth-graders, you can handle some Advanced Thinking. Look back over the mystery operations. Which ones are commutative? Associative? Does it even make sense to think about the distributive property with them? How would you go about inventing an operation that commutes?

Send your solutions to You can even send another solution to this same problem if you'd like!

Which some students did. And they found a different solution. How different is it? What do you think?

We are 4 eigth graders from Fayette County West Virginia. (Brittni, Bridgette, James, and Jessica)

We found a different solution to the Mystery Op 4.

If you subtract one from the first digit, then multiply it by the second digit, then add what you got when you subtracted one from the first digit, you get the solution.

y = first digit
z = second digit

(y - 1) * z + (y - 1) = solution

For example: (6 - 1) * 2 + (6 - 1) = 15

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