this post was submitted on 24 Nov 2024
389 points (98.3% liked)

xkcd

8888 readers
57 users here now

A community for a webcomic of romance, sarcasm, math, and language.

founded 1 year ago
MODERATORS
 

Look, you can't complain about this after giving us so many scenarios involving N locked chests and M unlabeled keys.

https://explainxkcd.com/3015/

you are viewing a single comment's thread
view the rest of the comments
[โ€“] givesomefucks 9 points 3 days ago (12 children)

Xkcd is smart, so I'm likely missing something.

But a random 2 out of 10, just roll two d10s and call it a day.

[โ€“] Mozingo 18 points 3 days ago (11 children)

2d10 would be used if each arrow had a 10% chance of being cursed. But that's not the case. There are 10 arrows, five are cursed, and 2 are selected. Therefore the first arrow would have a 5/10 chance of being cursed, while the second selection would have either a 4/9 or 5/9 chance of being cursed depending on whether or not the first arrow was cursed.

To solve this, requires using combinatorics. There are 10 choose 2 (45) ways to choose two arrows, of which there are 5 choose 2 (10) ways to choose 2 arrows that are non-cursed. This works out to be 2/9 odds to pull two safe arrows. Which means you need to get funkier with the dice.

load more comments (8 replies)
load more comments (8 replies)