01162013, 09:50 PM


When I teach functions, I draw a big box on the board, complete with gears, dials, needles, and buttons. I show a big funnel on the left going into it and then there's a little slide on the right that the empties out. The input (parameter) of the function goes "in" the function and the output (result) comes out the slide. I explain that there are workings inside the box that I drew that does the same thing to every input ("every legal input" is more accurate, but that's not the purpose here). I put a 10 in and an 8 comes out. I put a 85 in and an 83 comes out. Then, I ask, "If I put in a 54, what comes out?" And they shout out "52." I tell them that my machine is a "subtract 2 machine" and it's a function. I emphasize that for any value going in, there is only one value of the output. Now there may be more than one input that causes the output, but there is never more than one output for a certain input.
What sort of functions can you show?
I like Paul's conversion idea. This can be done with distances, temperature, etc.
How about 25% percentoff sales? You put in $100 and out pops $75.
Or, sorting girl and boy? When you put in Tom, out comes "male." When you put in Sally, out comes "female." Put in Peter, out comes "male" again. It's okay that two (or more) inputs spit out "male," but any one input can only be male OR female.
Or a lettergrade assigning function? You put in a 53 and out comes an F. Put in a 94 and you get an A.
Project? A quick one would be for the kids to dream up functions and have kids guess what the function is.
