Thursday, October 7, 2010

Flaw of Averages: pay per week

It is my pleasure to have Dave Martin guest blog today. He is a high school math teacher.

By Dave Martin

John was interviewed for a job at a factory where the management consisted of Dave, his brother, and 6 relatives.  The workforce consisted of 5 foremen, and 10 workers.  Dave informed John that the pay was well here, with an average salary of $600 per week.

After one week of work, John was upset as he only was paid $200.  John stormed into Dave's office, and accused Dave of lying.  Dave, the magical mathematician, explained, "Every week I get $4800, my brother gets $2000, my six relatives make $500, each foreman gets $400, and the ten workers get $200.  Averaging to a salary of $600 per week."

Unless, we talk about mean, median, and mode, the AVERAGE, can be meaningless.

If you use averaging to calculate student grades, how does this story affect your assessment practices?

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