Democratic Sentinel, Volume 18, Number 23, Rensselaer, Jasper County, 22 June 1894 — LIGHTNING CALCULATING. [ARTICLE]

LIGHTNING CALCULATING.

One-third la Memory, One-third Fraction and One-third Trick. One-third memory, one-third prao tice, and one-third trick—-that Is th« secret of most of the rapid calculators who figure before the public, says London Tit-Bits. There are very few calculations of which there Is not a short way to the solution, but perhaps none of them Is so easy and at the same time so surprising to the ordinary mind as the instantaneous extraction of the cube root. This Is a feat which has gained great applause for its performers from the days of Hutchins, “the lightning calculator,* till now. The extreme rapidity with which it Is worked, and the difficulty of the solution by the ordinary methods, render It one of the most taking of feats. Before explaining the method of performing this extraction of the cube root, It may be well for the benefit of those readers who have.forgotten some of their early school knowledge to explain what a cube root la Multiply a number by itself and the product by the original number, and the result is a cube. Thus 9xo equals 81 (the square of 9); 81x9 equals 729 (the cube of 9). Then 9 is the cube root of 729. Now for the method. First you obtain from-one of the audience an exact cube of not more than six places of figures, though with moderate practice the latter condition need not be insisted on. Say the cube given is 140,608, of which the root is 52. You know the cubes of the units by heart, thus: The cube of 11* j The cube of 2 is t Tue cube of a is 21 The cube of 4 is ' 64 The cube of 6 is m The cube of 6 is 216 The cube of 7 is 846 The cube of 8 is BIS The oube of 9 is ; S2l Now, as the thousands In the cube given exceed 125 and are less than 216, the tens in the reply must be 5. For the second figure, or units, a curious trick comes In. The cubes of 1,4, 5,6, and 9 end In the same figures; the cube of 2 Is 8; the cube of 3 ends In 7, and reversely the cube of 8 ends In 2 and the cube of 7 In 3. So when the questioner says 140,000, you say to yourself, 50; 608, you say out loud on the Instant, 52. Take another, 39,304. The thousands exceed 27; therefore the root is thirty something. The last figure Is 4; therefore the root Is 34.