Half Plus Seven

We’re evaluating expressions. Plug x = 7 into 5x – 3 and see what comes out the other end, that sort of thing. Instruction has the tendency here to get really rote really fast. Needless to say, worksheets abound for this unit.

So instead we spent some time in the Half Plus Seven function, for which no Wikipedia entry exists, and which therefore deserves a quick explanation:

Say you’re looking to date some sweet young thing. The issue here hinges on the adjective young, because, while you can never date anyone too sweet, you can certainly date someone too young.

So to determine if he or she is too young for you, take your age, divide it by two, and add seven. If he or she clears that bar, then, what questionable mathematics hath joined together, let no man put asunder.

So I had them plug in their own ages. We’re a bunch of 14- and 15-year-olds, which give minimum ages of 14 and 14.5, respectively. We had a conversation there about domain and where the function fails us, how a 13-year-old from SLV Middle is definitely fair game for a 14-year-old freshman from SLV High. We took it to absurd lengths, determining the minimum acceptable age for a 0-year-old newborn to be 7 years old, which, we all agreed, was plainly dumb.

I gave them my own minimum dating age and we worked backwards through the function to find my age, which, for whatever reason, is always good times for them. Next year, if I remember, we’ll evaluate some notable May-December celebrity couples and condemn them, should questionable mathematics demand it.

There is a comment to be made here about NCLB, stifled creativity, and the nonequivalence of the two, but TMAO is already there.

I'm Dan and this is my blog. I'm a former high school math teacher and current head of teaching at Desmos. More here.


  1. I’d suspect Maxim magazine before any religious text. Couldn’t find anything, in any case.

    Rick, until now I hadn’t blinked at the pairings at that end of the domain. I wonder if the only useful domain here is the mid-20s, the time when most dating actually happens.