It’s been custom written for the site and is quite neatly tied into the CMS and overall site.

Let’s say, hypothetically speaking, you met someone who told you they had two children, and one of them is a girl. What are the odds that person has a boy and a girl?

The correct answer is 2/3 but initially I fell into the trap of thinking it was 1/2. I want to clarify why this is the case in an attempt to convince my own brain why it was wrong.

The explanation and comments over on Coding Horror say a lot of things but what I’m going to do is explain how I convinced myself of the correct answer.

—–

Let’s start some basic probability.

The probability of a mother giving birth to a girl is 1/2, and the probability of a boy is 1/2.

The probability of a mother giving birth to a girl and then a girl is 1/2 * 1/2 = 1/4.

The probability of a mother having two children of the same sex is 1/4 (two girls) + 1/4 (two boys) = 1/2.

—–

Now let’s think about the question.

The mother can give birth to two children in 4 different ways, BB, BG, GB, GG (B = Boy, G = Girl).

We’ve been given the information that one of the children is a girl. Three of the states where at least one of the children is a girl and two of those also contain a boy. Hence we can say the probability of the other child being a boy is 2/3.

At least that’s how I understand it.

>> g.groups.zip([1,2], [3,4]) {|a,b,c| p a.inspect + ‘, ‘ + b.inspect + ‘, ‘ + c.inspect }
“[#<Group id: 1>, 1, 3], nil, nil”
“[#<Group id: 2>, 2, 4], nil, nil”

This is strange, I can no longer access the three elements of the array directly in the block. So I tried the following

>> g.groups.to_a.zip([1,2], [3,4]) {|a,b,c| p a.inspect + ‘, ‘ + b.inspect + ‘, ‘ + c.inspect }
“#<Group id: 1>, 1, 3″
“#<Group id: 2>, 2, 4″

As you can see this solved the problem, but I was confused why there was a difference so I executed…

>> g.groups.class
=> Array

Why when I cast it to an Array, from an Array, is it acting differently? Rails must have done something to the Array class that is returned by the has_many relationship.

Jamie

Originally uploaded by Dom Wrapson

Went riding this weekend with Dom and some guys from ChocolateFoot.

Discovered some new lines down Surrey hill I’d not ridden before with some sweet berms and tables.

Came back plastered in mud but it was a great ride.

Since I can remember I’ve been a core part of bit-tech. I joined the website when Koolvin, Moose, RTT and myself looked after the site featuring Koolvins mods and a few guides and reviews. The team behind the site has evolved from the core and the site formed a company in 2005. I developed the current site and CMS over a year ago and it’s been evolving ever since.

bit-tech moved into new premises in April this year and now the company has been sold to Dennis Publishing. I am no longer a shareholder and at some point in the future we shall be moving to the Dennis headquaters in London

I will be integrating with the Dennis development team over the next six months and hopefully the site will see some positive moves forward.

I’m now busy trying get more airtime on my mountain bike.

I just hope it’ll get off the ground!

I’ve also moved my blog and hosting for h4x.co.uk to the same UK hosting company and I’ve just updated my wordpress install to the latest version which is very fancy.

Not only that but we’ve also moved offices. Since TrustedReviews was acquired by IPC media bit-tech has found new offices and we moved in on Monday 1st April 2008. You will find images and words on the topic here.

That’s all for now!