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Vamshi Jandhyala

Books · Number Puzzles

Chapter 18

Nine Digits, the Unit Fractions

Using each of the nine digits 11 to 99 exactly once, some in the numerator and the rest in the denominator, write a fraction equal to 12\frac12. Then do the same for 13\frac13, 14\frac14, 15\frac15, 16\frac16, 17\frac17, 18\frac18 and 19\frac19.

Solution

One solution for each, though there are others: 12=672913458,13=583217496,14=394215768,15=269713485,16=294317658,17=239416758,18=318725496,19=638157429.\begin{aligned} \frac12 &= \frac{6729}{13458}, & \frac13 &= \frac{5832}{17496}, & \frac14 &= \frac{3942}{15768},\\[0.4em] \frac15 &= \frac{2697}{13485}, & \frac16 &= \frac{2943}{17658}, & \frac17 &= \frac{2394}{16758},\\[0.4em] \frac18 &= \frac{3187}{25496}, & \frac19 &= \frac{6381}{57429}. & & \end{aligned} In each, the four-digit numerator times the whole number on the left gives the five-digit denominator, and between numerator and denominator the digits 11 to 99 each appear once. For instance 6729×2=134586729 \times 2 = 13458 and 6381×9=574296381 \times 9 = 57429.