The Life and Times of Florence Knitingale

Tuesday, October 31, 2006

P(A+B) = P(A) X P(B)

Warning: This page contains graphic mathematic content, as well as some amount of shameless showing off. Reader discretion is advised.

Sven has 2 pairs of blue jeans and 3 pairs of khaki pants. He also has 5 blue shirts, 4 red shirts, and 3 tan shirts. Resisting the urge to point out the obvious truth that Sven needs a new wardrobe advisor (12 shirts in 3 colors??? Please.), and assuming that he picks out his clothes at random, what is the probability that he will wear blue jeans and a red shirt?

(I added the part in about the wardrobe advisor….you probably didn’t guess that….)

This was the bonus question on my Statistics test yesterday. And the above formula, which I cleverly pulled out of the carefully organized and well educated storage in my mind (out of my ass, desperately, after trying about 12 other things) was the correct way to solve it. I know, because when I turned it in I told Mr. Guillford that I was pretty confident about the test but unsure about Sven’s wardrobe. So he kindly looked at that problem and said “Well, you got it right.” (Insert happy dance of choice here.) Okay, so I know that I don’t have the rest of the test back yet and chances are that this problem is actually painfully easy and I look like a dork for being excited to know it—but I’ve been dreading this class and am utterly amazed to find myself (kind of) enjoying it. The formula, in case you care at all, translates out to “the probability of event A and event B happening at the same time is equal to the probability of A times the probability of B”. I do think, however, that there are some notable quirks in probability logic. For instance:

The probability that I will be ready to divide the stitches for Samus (event A) times the probability that I will actually have the large stitch holder with me (event B) apparently equals zero. Hence the fact that I ended up cramming 144 stitches on a holder intended for something like a sleeve last night at Knit for Life. I’ve changed it out now and here’s the progress to date:

I still love this beyond reason, and I still want to wear it right this minute. Mr. K is on board with that. Yesterday I asked him what would go with the pants in my hand (where’s Sven when I need him?) and he said “Oh, that cardigan you’re making would go perfectly!” Cool. I’ll just whip downstairs and finish that before school starts, shall I?) But I digress. Back to those fascinating probabilities (work with me, here—I HAVE to think they’re fascinating):

The probability that I will lose a darning needle (event A) times the probability that it will be my last one (event B) times the probability that it will be raining and I won’t want to run to the store for another package (event C) always equals 100%. Always. Definitely a statistical anomaly.

The probability that I will be running late for school (event A) times the probability that every pair of reasonable pants I own will be in the wash (event B) is at least 95%. Multiply that times the probability that my windshield will need scraping and you’ve got yourself an even 100%.

Or how about this: The probability that the Seahawks will do something uniquely brilliant (event A, becoming less likely as the season wears on) times the probability that I will be looking down at my knitting (event B). Again, 100%.

The probability that I will be eating something staggeringly unhealthy (event A, and let’s not discuss the fact that this may be a 100% probability all on its own, shall we?) times the probability that someone will walk by who I respect and would not wish to have see me eating pretzels stuffed with some sort of processed cheese product (event B, and admittedly disgusting and shameful). Absolutely 100%.

The probability of the cat running off with the yarn (event A) times the probability that the yarn will be attached to something important (event B) times the probability that I won’t have a good hold on the other end (event C) times the probability that the item is very complicated (event D) times the probability that the item was nearly complete (event E). Sadly, tragically, 100%. Last time it happened, it was lace. The probability that the cat survived was staggeringly low, but she beat the odds. I think throwing in “hugely cute” probably tipped them a bit in her favor.

All of our news today is leading with the story of a “cold snap in Western Washington”. Newsflash, guys: I don’t think of it as news, exactly, when I can go out side and figure it out by the frozen nose hairs. But I’m digressing again. It is, in fact, a very, very cold day (the kind my mother used to call “colder than a well digger’s ass”, which makes me pity well digger’s wives everywhere) so I thought I’d show you our white, crispy yard.

Think I'll go sit by the fire with a warm cat and some knitting (like the probability of that isn’t through the roof whether it’s alarmingly cold or not).


  • At 11:04 AM, Blogger Charity said…

    Just the title of this post made my head spin! Yikes - glad to hear you remembered the formula when you needed it. :0)

  • At 11:45 AM, Anonymous Marianne said…

    Yep, you rock'em hard!
    (I am just so proud of you!)
    I'm so glad to know your cave is so warm and cozy. Mercy, frozen nose hairs, they feel so strange.

  • At 12:44 PM, Anonymous Marianne said…

    Samus looking so very pretty. I understand the affection.
    Great deck!


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