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Calculate the number 891

NUMBERMANIA: Calculate the number 891 using numbers [2, 4, 5, 4, 29, 130] and basic arithmetic operations (+, -, *, /). Each of the numbers can be used only once.

Correct answers: 3

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B.J. Novak: Learned Nothing in College

I learned nothing in college. It was really kind of my own fault. I had a double major: psychology and reverse psychology.

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Heinrich Daniel Ruhmkorff

Born 15 Jan 1803; died 20 Dec 1877 at age 74.German mechanic, instrument maker and inventor whodevised the Ruhmkorff coil, his version of the induction coil (after Nicholas Joseph Callan's earlier invention of 1836). Ruhmkorff's induction coil could produce sparks over 1 ft (30 cm) in length, and became popular for energizing discharge tubes, especially those for generating X-rays (discovered by Wilhelm Röntgen, on 8 Nov 1895). The device uses a primary coil and iron core concentric with a secondary coil with a large number of turns. By using a contact breaker giving abrupt and rapid interruptions in the primary coil current, a concentrated, changing magnetic field produced a high voltage in the secondary coil. He also invented a thermo-electric battery in 1844.«

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