Ancestors

Written by Stuart Langridge on 2025-01-04 at 09:35

Maths people, help!

In "Scarne on Cards", John Scarne discusses the odds for a game. He says this:

"The chances are 12220 to 9880 in their favour. [These numbers are definitely correct -- sil] That is, the percentage in their favour is 10-1/123."

Where's he getting that percentage from? How's he doing the calculation? I can't end up at that number, so I must be doing something wrong...

=> More informations about this toot | More toots from sil@mastodon.social

Written by Stuart Langridge on 2025-01-04 at 18:43

Ok, our conclusion to this little puzzle is “Scarne did the calculation wrong”. The number is 2340/22100, which is an edge of about 10.58%, not “10-1/123” (which is about 10.081%).

This being an error is bolstered by further research: in his later Scarne’s Complete Guide to Gambling, he relates the same game (with a different story about it), lays out the same calculation, and comes up with an answer of 10 1/17% which isn’t right either!

Still, be tolerant: life is hard pre-calculators.

=> View attached media

=> More informations about this toot | More toots from sil@mastodon.social

Written by Stuart Langridge on 2025-01-04 at 19:02

it's not all that hard, though. Admittedly he's doing this in the context of writing a big long book, but didn't they have editors in the 50s? I -- no aficionado of long division -- just spent all of five minutes doing the calculation on paper and there it is, ~10.58%.

(I don't even know how you do this division to end up with a fraction rather than a decimal. Someone who was doing maths by hand in the fifties (and presumably learned to do so in the 1910s) will have to tell me (by ouija board).)

=> View attached media

=> More informations about this toot | More toots from sil@mastodon.social

Written by James Henstridge on 2025-01-04 at 23:19

@sil my guess is that he might have been using a slide rule, but I'm not altogether certain how you'd do the "closest simple fraction" thing. Both incorrect fractions are "1/something" so maybe he was trying to calculate an inverse?

=> More informations about this toot | More toots from jamesh@aus.social

Written by Stuart Langridge on 2025-01-04 at 23:20

@jamesh ooh slide rule. I didn’t think of a slide rule. Never used one :)

=> More informations about this toot | More toots from sil@mastodon.social

Written by Marcos Dione on 2025-01-04 at 23:27

@sil @jamesh slide ruler*?

=> More informations about this toot | More toots from mdione@en.osm.town

Written by James Henstridge on 2025-01-04 at 23:29

@mdione @sil One of these things: https://en.wikipedia.org/wiki/Slide_rule

=> More informations about this toot | More toots from jamesh@aus.social

Toot

Written by Marcos Dione on 2025-01-04 at 23:35

@jamesh @sil exactly. My father had one. He never taught me how to use it. We either lost it, broke it or both :(

=> More informations about this toot | More toots from mdione@en.osm.town

Descendants

Written by Marcos Dione on 2025-01-04 at 23:38

@jamesh @sil oh, they are called slide rule? Not ruler? Because my father's has a metallic edge with centimeters and millimeter etched into it to measure and draw straight line. In Spanish they're called "regla de cálculo", 'calculation ruler'.

=> More informations about this toot | More toots from mdione@en.osm.town