Real Functional Maths

I like maths. I like maths because it's useful, but sometimes in class that is not always obvious. Imagine my delight when I got this email from my little brother (OK, he's 26, but compared to me..).

So we're having a little trouble working out a backup plan should the ash cloud ground our flights next month... we plan on booking a backup coach/train combo to get to barcelona in case Vatnajokull kicks off again.

The plane fare is refundable if the ash kicks off - its price is £75.

For the coach/train, we have two options. One is half refundable - total price £100, but £40 of that is refundable. The other is fully refundable - total price £159.50, all of that refundable.

We're putting the odds of Iceland ruining things at 50/50, so which one train fare is best - half or full - to get based on the prices involved?

This got me thinking. Partly thinking about how to solve the problem, and partly "ooh - that's a good lesson idea".

Anyhow, here is the spreadsheet I wrote ...

The full link is here...

Now all I need to do is turn it into a lesson. Modelling, excel skills, researching prices, ...

I feel a bit let down by the technology.

I always feel a high tech solution should be better (more efficient, slicker, make me look better) than a low tech one. With that in mind when planning to collect heights of Y9 to do some serious stats with, I decided to set up a motion sensor in the top of the doorway, and measure the distance to the floor.

Then as students arrive, they stand in the doorway (no heels please), and the sensor measures the distance to the top of their heads. They type that in to a Google Form (along with Age, gender, and some other bits), and then the spreadsheet subtracts one from the other to give their height.

This should have been fool proof. Yeah, right.

Sensor in doorway. Check.

It measures 2.04 m to the ground. Check with tape measure. Check.

I stand underneath, subtract reading from 2.04m to get my height. It tells me I'm 186 cm - 6'1" (according to Wolfram|Alpha).

The problem? I'm 6'3". Double check against my known kids heights. It puts them down 2 inches (and Pippa was measured by school nurse recently). Check with the missus - it puts her short too, by an inch and a half (and she checked at the gym recently).

I can't work out how it could possibly be wrong, but it is.

So my lesson plan goes back to having a metre ruler on the wall, which upsets me more than is reasonable! At least I'm still using GoogleForms to collect the data. That's progress at least.