Looking at Stats and Probability School Rumble Style

OK I told you guys I was leaving right? But I couldn’t bear the thought of 9 days without any School Rumble merchandise, so I went to this neighbourhood store, the daylight-robbing Comics Connection, where they were selling the School Rumble Keychains from Alter for double the retail price. These were still sealed in boxes, so I didn’t know what I was buying.

There are ten different types.

And I chose to take a chance.

I wanted Eri, Yakumo and Akira, so that means five out of ten of these were acceptable, a 50% chance. I bought one. IT WAS BIKINI MIKOTO FUCK. I walked right back into the store and bought a second one. IT WAS KAREN! Damn. I’m ok with Karen but somehow, she’s not my type.

So I actually got the worst possible combination actually. 5/10 x 4/9 = 2/9. I had a 22 percent chance of failing to get even ONE girl that I wanted. And I got this 22 percent.

The chances of getting one crappy chain (Mikotos, Sara, Tenma and Karen) and then one desired chain was 5/10 + 5/10 x 5/9 which is about 78 percent!! Or you could just take 100-22.

IT’S A FUCKING OMEN!! Actually, I should’ve just bought one more. Then the chances of not getting what I wanted would be very very slim. 5/10 + 5/10 x 5/9 + 5/10 x 4/9 x 5/8 = about 92 percent!!! Nobody fails at 92 percent!

Hmm but upon closer examination, the fact that I had already failed twice means that if I bought the 3rd one, my chances of getting a good keychain would actually be only 5/8, that is 62.5 percent, rather than 92 percent.

I thought this while on the way home. But then again, I’m probably getting the whole set upon my return to Singapore so less duplicates the better.


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