BRAIN TEASERS

# Find number abc

If ab3c2 + 78307 = bb96c9 find number abc. Multiple solutions may exist.
The first user who solved this task is Djordje Timotijevic.
#brainteasers #math

### I Know the Truth

At school, Little Johnny was told by a classmate that most adults hide at least one dark secret and this makes it very easy to blackmail them merely by saying, "I know the whole truth."
So Little Johnny decides to try it out. When he arrives home from school that day, he says to his mother, "I know the whole truth." His mother looks shocked, quickly finds \$20, and gives it to him, saying, "Just don't tell your father."
Quite pleased, Little Johnny waits for his father to get home from work, and greets him with, "I know the whole truth." His father looks shocked, quickly finds \$40, and gives it to him, saying, "Just don't tell your mother."
The next morning, Little Johnny is on his way to school when he sees the mailman at his front door. The boy decides to try again. "I know the whole truth."

The mailman drops his mailbag, throws opens his arms, and says, "Then come give your real daddy a nice big hug!"

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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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