### Challenge 104

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Calculator keys Difficulty level: A calculator has two keys: D, which doubles the number, and T, which erases the number of units. If a person writes 1999 and then press D, T, D, and T in sequence, which number will it be? Challenge 38 I squared a number… Challenge Index Next >> Challenge 40 Who is the big brother?
Wednesday, February 20, 2002 was a historic date. For a minute there was a conjunction of numbers that only occurs twice a millennium. This conjugation occurred exactly at 20 hours and 02 minutes of February 20 of the year 2002, ie 20:02 02/02 2002. It is a symmetry that in mathematics is called capicua (digits that give the same number when read from the left to the right, or vice versa).
It is noteworthy that the third major interval obtained by Arquitas agrees with that present in the Harmonic Series. Such a phenomenon leads us to imagine that Architas had a sensitive ear when he realized that the third corresponding to (4/5) - lower than Pythagorean, (64/81) - sounded more natural, since it merged exactly within natural harmonics. of a note.
5. Mathematics in the Emergence of Temperament Temperament in the general sense means a scale in which all or almost all intervals are slightly inaccurate but undistorted. They end up valuing certain intervals over others, in the sense that the former correspond to the same frequency ratios as the others.
The beggar and the cigarettes The answer is 14 cigarettes. As the beggar needs 6 ends to form a cigarette, with the 72 ends found he can make 12 cigarettes. After smoking them, there will be 12 more tips left, with which he can make 2 more cigarettes, thus completing the 14 cigarettes. Back to statement Challenge 179 Secret operation Challenge index Next >> Challenge 181 Adding six
4.2. Science / music in Mersenne Mathematician, philosopher and theoretical musician, Marin Marsenne (1588-1648) is one of the leading French thinkers of the 17th century, whose work - mostly devoted to the science, theory and practice of music - takes over. central role in the scientific and academic movements of the time.