MathDB

18

Part of 2019 AMC 10

Problems(2)

Repeating Decimals in a Base

Source: 2019 AMC 12A #11 / AMC 10A #18

2/8/2019
For some positive integer kk, the repeating base-kk representation of the (base-ten) fraction 751\frac{7}{51} is 0.23k=0.232323...k0.\overline{23}_k = 0.232323..._k. What is kk?
<spanclass=latexbold>(A)</span>13<spanclass=latexbold>(B)</span>14<spanclass=latexbold>(C)</span>15<spanclass=latexbold>(D)</span>16<spanclass=latexbold>(E)</span>17<span class='latex-bold'>(A) </span> 13 \qquad<span class='latex-bold'>(B) </span> 14 \qquad<span class='latex-bold'>(C) </span> 15 \qquad<span class='latex-bold'>(D) </span> 16 \qquad<span class='latex-bold'>(E) </span> 17
AMC 10AMC 12AMC2019 AMC 12A2019 AMC 10A2019 AMC
Mind-changing Henry

Source: 2019 AMC 10B #18

2/14/2019
Henry decides one morning to do a workout, and he walks 34\tfrac{3}{4} of the way from his home to his gym. The gym is 22 kilometers away from Henry's home. At that point, he changes his mind and walks 34\tfrac{3}{4} of the way from where he is back toward home. When he reaches that point, he changes his mind again and walks 34\tfrac{3}{4} of the distance from there back toward the gym. If Henry keeps changing his mind when he has walked 34\tfrac{3}{4} of the distance toward either the gym or home from the point where he last changed his mind, he will get very close to walking back and forth between a point AA kilometers from home and a point BB kilometers from home. What is AB|A-B|?
<spanclass=latexbold>(A)</span>23<spanclass=latexbold>(B)</span>1<spanclass=latexbold>(C)</span>115<spanclass=latexbold>(D)</span>114<spanclass=latexbold>(E)</span>112<span class='latex-bold'>(A) </span> \frac{2}{3} \qquad <span class='latex-bold'>(B) </span> 1 \qquad <span class='latex-bold'>(C) </span> 1\frac{1}{5} \qquad <span class='latex-bold'>(D) </span> 1\frac{1}{4} \qquad <span class='latex-bold'>(E) </span> 1\frac{1}{2}
AMCAMC 10AMC 10 B