Test results poser

I've got to the point that I get really excited about interesting maths problems (this might not be a new issue, but being a teacher allows me to unashamedly embrace the inner geek), and I came across this one a couple of days ago:

A disease has broken out in the world, which infects on average one in every 1000 people. The onset has no physical symptoms in the early stages, but medics have developed a test that is able to detect the disease with an accuracy of 95%, or more precisely, the test will return positive with 100% accuracy if the person tested is infected, but will return a false positive (i.e. will say the person is infected when in fact they are not) 5% of the time if the person is not infected. 

You take the test, and the result is positive. What is the probability that you are infected with the disease? Is it:

(a) 100%

(b) 95%

(c) 2%

Answers on a postcard (or a comment, if you must) with explanation. I'll reveal the answer some time in the future...

There may not be a God, but ostriches definitely exist

Earlier in the week, as I was travelling up to a friend's, I picked up a copy of The Guardian (it seems I've become like that...) to pass the journey, and stumbled upon this article by Polly Toynbee. Now it's this sort of article that could spawn a thousand blog posts (and for all I know, already has), but I shall limit myself to comment on the slogans the British Humanist Association has decided to print on buses:

"There's probably no God. Now stop worrying and enjoy your life."

I'm guessing the intention to be a counterbalance to the bible verses put up by the Trinitarian Bible Society, a nice little message to not get caught up in all this "religion" and to get on with life in the present. Except I don't think it really gets there - after all, this is meant to be a counterthrust to those who claim there is a God who is worth bothering about, and moreso that:

"It is a fearful thing to fall into the hands of the living God."

Hebrews 10:31

Now, if that's the two arguments, I really, really do not want the word "probably" to still be there before I "stop worrying and enjoy my life". The phrase "smile, it might never happen" seems a little patronising and lacking in comfort when the worry is about some variety of minor stress, and I am a little astonished to see the British Humanist Association using an equivalent to casually pass over matters of eternal significance.

I want to stop before I start to sound like I'm presenting some form of Pascal's Wager, or making Christianity sound like all it has to offer is a psychological feeling of security, both of which I feel does not do justice to the truth and beauty of the message gospel, but it is simply interesting to note that the offering of the leading "freethinking" society in this country is that we can't be sure but let's not worry our pretty little heads about such lofty things...

For unto us a child is born

“Fear not, for behold, I bring you good news of a great joy that will be for all the people. For unto you is born this day in the city of David a Savior, who is Christ the Lord.”

Luke 2:10-11

Great news! Wishing you all a very merry Christmas, a Saviour has come!

“There is therefore now no condemnation for those who are in Christ Jesus. For the law of the Spirit of life has set you free in Christ Jesus from the law of sin and death. For God has done what the law, weakened by the flesh, could not do. By sending his own Son in the likeness of sinful flesh and for sin, he condemned sin in the flesh, in order that the righteous requirement of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit.”

Romans 8:1-4

Signs that I'm still a not from round these parts, no. 1 - The Trains

I've figured out that I really don't understand the ticketing system for National Rail. I've been checking prices of tickets to go up to Durham (those with ears to hear...), and was under the assumption that the further you book in advance the cheaper it would be. So as a test, I entered a date for 12 weeks away, and was quoted a price of £70ish - not ideal. It was only then that I realised that that was for an "anytime" ticket, and it hadn't offered any advance tickets. So I knocked the date back a month, and got quoted £25ish - much more reasonable.

So to get the right fare, do you book in advance, but not too much in advance? Why is this starting to feel like buying something on eBay?

I'm now waiting to see Imhotep on the exam papers...

As it was the last week of school, I was taking a laid back approach to my classes, taking time to watch some videos and generally relax before the end of term. I decided as a bit of a joke to show this to some of my classes, not letting on the genre:



At the end of the class, I asked my Year 11s:

"OK, you can admit it, how long did it take you to work out it was a spoof?"

To which they responded:

"A spoof, sir?"

Oh dear...

Home, where my thoughts escape me...

Well, I'm now back in Belfast after surviving my first full term, feeling somewhat shattered and ready for a rest. To aid in this, I have brought exactly no work home with me, and I don't have much reason to feel guilty about having done so, so what lies ahead for the next few days is one of rest, a little personal study and reading, and meeting of old friends. Should be fun.

As all good things do, it won't last forever, travel back is before New Year and there is moving and preparation to be done, but that can definitely wait for a few days...