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Calculate the number 5315

NUMBERMANIA: Calculate the number 5315 using numbers [3, 9, 3, 4, 40, 721] and basic arithmetic operations (+, -, *, /). Each of the numbers can be used only once.

Correct answers: 27

The first user who solved this task is Sanja Šabović.

#brainteasers #math #numbermania

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Fetch A Nice Price

I took a stuffed dog to the Antiques Roadshow and was told, "This is extremely rare. Do you know what it would fetch in good condition?"
"Dunno," I said. "A stick?"

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Crystal rectifier

In 1874, a paper by Ferdinand Braun (1850-1918) was published in the Annalen der Physik und Chemie describing his discovery of the electrical rectifier effect. He observed that certain crystals of metal sulphides have a larger or smaller resistance to an electric current, depending on its direction of flow. He used a galena crystal, a semiconductor material composed of lead sulfide. He found the rectifying effect especially true if at least one of the electrodes was a pointed wire. Thus, he had discovered the point-contact rectifier effect, the first semiconductor device. This effect wasn't used until over 30 years later in the form of the “cat's whisker”crystal radio detector which ultimately led to the point-contact transistor first produced in 1948.

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