Replace the question mark with a number
MATH PUZZLE: Can you replace the question mark with a number?Correct answers: 490
The first user who solved this task is Vladimir Krnac.
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Musical ArcsIn 1900, Nature reported the Musical Arcs invented by William Du Bois Duddell, an English physicist. By means of an arrangement of electric currents he produced a musical note from an arc lamp that could be altered to any pitch is obtained and a tune played. This may be regarded as the first fully electric instrument. While investigating the noise produced by the operation of carbon arc lamps - anything from a low hum to a high-pitched whistle - he found that adding resonance circuits adjusted the pitch of the sounds. His Singing Arc demonstrated this phenomenon using a keyboard connected to an arc lamp, giving audible results without any amplifier. He toured the country with his Singing Arc, as a novelty performance.«* |