Calculate the number 890
NUMBERMANIA: Calculate the number 890 using numbers [8, 2, 4, 7, 28, 839] and basic arithmetic operations (+, -, *, /). Each of the numbers can be used only once.Correct answers: 2
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Spirit levelIn 1666, Robert Hooke invented the spirit level, according to Sir David Brewster in the 1832 Edinburgh Encyclopedia. It was likely a variation on the spirit level, or “artificial horizon,” which he may have used while employed as City Surveyor of London after the Great Fire. The original concept was due to Melchisédech Thévenot, sometime before 2 Feb 1661, the date of his letter about it to Christiaan Huygens. In the 1670s, Hooke added a spirit level to his quadrant.« |