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Ran across this interesting clock:

https://www.thinkgeek.com/product/kjpm/#tabs

With a price of \$149.99 I think it's the price that needs some math, but it is interesting. I can only think of how confused one would be when using it as an alarm clock and you first look at the clock after shutting the alarm...
Is this symbol for division unique to that clock, or is it commonly used by people somewhere?

The colon is used to represent ratios and division in Dutch textbooks, at least at primary school level. I assume it's used elsewhere in Europe as well, but I'm not sure about where exactly it is or isn't.
Hello!

(04-07-2019 10:31 AM)Thomas Okken Wrote: [ -> ]The colon is used to represent ratios and division in Dutch textbooks, at least at primary school level. I assume it's used elsewhere in Europe as well, but I'm not sure about where exactly it is or isn't.

I went to school in Italy but was mainly taught by German teachers. We also used the ":" colon for division. Alternatively the "/" forward slash. But never the colon with the dash that we find on calculator keyboards. On the rare occasions when I do a calculation on paper or write an equation I still use the ":" colon sign.

Regards
Max

NB: If I remember I will ask my son what he was taught when he went to primary school in the mid-2000 years.

Edit: Did a very quick Google search for contemporary primary school textbook calculus and found lots of stuff like this:
I've never encountered the ":" symbol for division (in USA), except in several prior discussions here in MoHPC, where it is consistently mentioned as the most common symbol used in some countries in Europe, while not in others, though I don't recall which were which.

From Wikipedia:

Quote: a ÷ b

This form is infrequent except in elementary arithmetic. ISO 80000-2-9.6 states it should not be used. The obelus is also used alone to represent the division operation itself, as for instance as a label on a key of a calculator. The obelus was introduced by Swiss mathematician Johann Rahn in 1659 in Teutsche Algebra.[10]:211

a : b

In some non-English-speaking countries colon is used to denote division.[11] This notation was introduced by Gottfried Wilhelm Leibniz in his 1684 Acta eruditorum.[10]:295 Leibniz disliked having separate symbols for ratio and division. However, in English usage the colon is restricted to expressing the related concept of ratios.
In Norway ":" is commonly used as division sign and in ratio (which is division anyway).

3:2=1,5 (Yes "," as in "one comma five", not the american "." so not "one point five")

In ratio; 10,1:1 "ten comma one to one (used f. inst. in engine comprerssion ratio).
(04-07-2019 12:59 PM)rprosperi Wrote: [ -> ]From Wikipedia:
Quote: a ÷ b

This is the form that I learned (1960's) and used in school in Quebec/Canada.
Later replaced (1980's) with / as electronic typewriter and then personal computer started being used by everybody.
(04-07-2019 01:55 PM)DA74254 Wrote: [ -> ]In Norway ":" is commonly used as division sign and in ratio (which is division anyway).

3:2=1,5 (Yes "," as in "one comma five", not the american "." so not "one point five")

In ratio; 10,1:1 "ten comma one to one (used f. inst. in engine comprerssion ratio).

Same here in Italy.
(04-07-2019 08:07 PM)Massimo Gnerucci Wrote: [ -> ]
(04-07-2019 01:55 PM)DA74254 Wrote: [ -> ]In Norway ":" is commonly used as division sign and in ratio (which is division anyway).

3:2=1,5 (Yes "," as in "one comma five", not the american "." so not "one point five")

In ratio; 10,1:1 "ten comma one to one (used f. inst. in engine comprerssion ratio).

Same here in Italy.

Just curious: when speaking, does one actually say "one comma five" (though obviously in your native tongue), or perhaps "one decimal five" ?

And I think it's English "one point five" not American, though being American, I am not sure.
Hello!

(04-07-2019 08:42 PM)rprosperi Wrote: [ -> ]Just curious: when speaking, does one actually say "one comma five" (though obviously in your native tongue)...

"Eins Komma Fünf" it would be in German. "Uno virgola cinque" in Italian (unless they changed that after I left). At work I am supposed to say "day-see-mal" but more often than not both pilots and air traffic controllers will say "point" instead.
(04-07-2019 01:55 PM)DA74254 Wrote: [ -> ]In Norway ":" is commonly used as division sign and in ratio (which is division anyway).

3:2=1,5 (Yes "," as in "one comma five", not the american "." so not "one point five")

In ratio; 10,1:1 "ten comma one to one (used f. inst. in engine comprerssion ratio).

Same here in Spain.

V.
.
Quote:Just curious: when speaking, does one actually say "one comma five" (though obviously in your native tongue), or perhaps "one decimal five" ?

In Spain we do read "1,15" as "uno coma quince", not "uno decimal quince".

V.
.
One random little difference between mainland Europe and (American?) English usage is that Europeans never drop a zero before the comma, as far as I know. So while 1/2 can be pronounced "point five" in English, or at least in American English, in Dutch you say "nul komma vijf," never "komma vijf."
(04-07-2019 08:42 PM)rprosperi Wrote: [ -> ]Just curious: when speaking, does one actually say "one comma five" (though obviously in your native tongue), or perhaps "one decimal five" ?

In Portuguese: “um vírgula cinco” (1,5), “três vírgula quatorze dezesseis” or “três vírgula um quatro um seis” (3,1416).

In Polish: “jeden koma pięć” (1,5), “trzy koma jeden cztery jeden” (3,141), (from Wisława Szymborska’s "Number Pi" poem.
(04-07-2019 01:55 PM)DA74254 Wrote: [ -> ]In Norway ":" is commonly used as division sign and in ratio (which is division anyway).

3:2=1,5 (Yes "," as in "one comma five", not the american "." so not "one point five")

In ratio; 10,1:1 "ten comma one to one (used f. inst. in engine comprerssion ratio).

Same in Brazil.

Not sure in Portugal.

Cheers

Level 5:

$$\sqrt{\frac{7}{22}\pi ^{7}}$$ min

Level 9:

$$\frac{\left ( \pi +\pi ^{2}+\pi ^{3}+\pi ^{4} \right )^{2}-\frac{9}{32}\left ( e+2\sqrt[3]{2} \right )}{50^{2}}$$ h
(04-07-2019 08:42 PM)rprosperi Wrote: [ -> ]Just curious: when speaking, does one actually say "one comma five" (though obviously in your native tongue), or perhaps "one decimal five" ?

And I think it's English "one point five" not American, though being American, I am not sure.

In French from Quebec.
Old peoples use the imperial system, so "un point cinq" or "1.5"
Young peoples use the metric system, so "un virgule cinq" or "1,5"
(04-08-2019 12:14 AM)Gerson W. Barbosa Wrote: [ -> ]
Level 5:

$$\sqrt{\frac{7}{22}\pi ^{7}}$$ min

Level 9:

$$\frac{\left ( \pi +\pi ^{2}+\pi ^{3}+\pi ^{4} \right )^{2}-\frac{9}{32}\left ( e+2\sqrt[3]{2} \right )}{50^{2}}$$ h

For both of these, but especially Level-9, by the time you figure it out, it's already a later time...
(04-07-2019 08:42 PM)rprosperi Wrote: [ -> ]Just curious: when speaking, does one actually say "one comma five" (though obviously in your native tongue), or perhaps "one decimal five" ?

"Un virgule cinq" in French (I'm bilingual), so yes, literally "one comma five."
(04-07-2019 08:42 PM)rprosperi Wrote: [ -> ]
(04-07-2019 08:07 PM)Massimo Gnerucci Wrote: [ -> ]Same here in Italy.

Just curious: when speaking, does one actually say "one comma five" (though obviously in your native tongue), or perhaps "one decimal five" ?

And I think it's English "one point five" not American, though being American, I am not sure.

En komma fem in Norwegian, meaning "one comma five". Tre komma fjorten (three comma fourteen). If there are more decimals, I personally recite them in pairs (three comma fourteen fifteen) or in singles (three comma one four one five nine two six five three five eight nine seven nine three two) if more than 5-6 decimals.
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