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Calculate the number 547

NUMBERMANIA: Calculate the number 547 using numbers [4, 9, 2, 5, 13, 130] and basic arithmetic operations (+, -, *, /). Each of the numbers can be used only once.

Correct answers: 3

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History Teacher:

History Teacher: "Why was George Washington standing in the bow of the boat as the army crossed the Delaware?"
Student: "Because he knew if he sat down, he would have to row."

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Arago announces electromagnetism

In 1820, Francois Arago announced that a copper wire between the poles of a voltaic cell, could laterally attract iron filings to itself (Ann. de Chim. et de Physique., xv. p.93). His discovery came in the same year that Oersted discovered that an electric current flowing in a wire would deflect a neighbouring compass needle. Arago in the same publication described how he had successfully succeeded in causing permanent magnetism in steel needles laid at right angles to the copper wire. Arago and André-Marie Ampère, discussed and experimented with forming the copper wire into a helix to intensify the magnetizing action. However, it was not until 1825 that the electromagnet in its familiar form was invented by William Sturgeon.«

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