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Calculate the number 2100

NUMBERMANIA: Calculate the number 2100 using numbers [9, 4, 9, 1, 39, 880] and basic arithmetic operations (+, -, *, /). Each of the numbers can be used only once.

Correct answers: 21

The first user who solved this task is Djordje Timotijevic.

#brainteasers #math #numbermania

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Play chess with bald men

'I like to play chess with bald men in the park, although it's hard to find 32 of them.'

Emo Phillips (February 7 1956-)

Picture: Matthew Simmons/Getty Images

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Valdemar Poulsen

Born 23 Nov 1869; died 23 Jul 1942 at age 72.Danish engineer who in 1903 developed the first device for generating continuous radio waves, thus aiding the development of radio broadcasting. His arc transmitter increased the frequency range of Duddell's Singing Arc (1900) from the audio range to radio waves, enabling speech to be transmitted up to a radius of 150 miles. By 1920 the Poulsen Arc transmitter was as powerful as 1000kW with ranges of up to 2,500 miles. An earlier invention was the Telegraphone, for which he filed a patent in Denmark on 1 Dec 1898. This was the first device in history to use magnetic sound recording, although this invention remained commercially impractical due to low sound output until the advent of vacuum tube amplifiers in the 1930s.[Biog. Dict. of the Hist. of Tech. gives date of death 23 Jul 1942. DSB and EB give Jul 1942.]

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