BRAIN TEASERS

# What is the missing number?

MATH PUZZLE: Can you replace the question mark with a number?
The first user who solved this task is Djordje Timotijevic.
#brainteasers #math #riddles

### Vacation

Billy Bob and Luther were talking one afternoon when Billy Bob tells Luther, "Ya know, I reckon I'm 'bout ready for a vacation. Only this year I'm gonna do it a little different. The last few years, I took your advice about where to go.
Three years ago you said to go to Hawaii. I went to Hawaii and Earlene got pregnant.
Then two years ago, you told me to go to the Bahamas,and Earlene got pregnant again.
Last year you suggested Tahiti and darned if Earlene didn't get pregnant again."
Luther asks Billy Bob, "So, what you gonna do this year that's different?"
Billy Bob says, "This year I'm taking Earlene with me."

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### First dated printed arithmetic book

In 1478, the anonymous Arte dell'Abbaco(“The Art of the Abacus”), printed in Treviso, Italy had this publication date. It is the first dated printed book on arithmetic. The unknown author was likely a priest, and it was dedicated to some of his young friends who kept asking for it. The printer was probably Geradus de Lisa, dé Flandria. The 124-page text dealt with commercial applications of arithmetic, so the language was the local vernacular Venetian dialect, not the scholarly Latin used for the abstract studies of universities. The book teaches the four main operations, with numerous examples, and the concept of fractions (but not the as yet unknown decimals). He shows how to calculate the date of the new Moon. Although some pamphlets on Algorithmus are possibly older than this book, they are undated.«[Image: detail of a calculation shown in the book.]
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