MathDB
Floors and Fractionals

Source: 2020 AMC 12A #25

January 31, 2020
AMCAMC 122020 AMC 12A2020 AMCAMC 12 Arelatively primenumber theory

Problem Statement

The number a=pqa = \tfrac{p}{q}, where pp and qq are relatively prime positive integers, has the property that the sum of all real numbers xx satisfying x{x}=ax2\lfloor x \rfloor \cdot \{x\} = a \cdot x^2 is 420420, where x\lfloor x \rfloor denotes the greatest integer less than or equal to xx and {x}=xx\{x\} = x - \lfloor x \rfloor denotes the fractional part of xx. What is p+q?p + q?
<spanclass=latexbold>(A)</span>245<spanclass=latexbold>(B)</span>593<spanclass=latexbold>(C)</span>929<spanclass=latexbold>(D)</span>1331<spanclass=latexbold>(E)</span>1332<span class='latex-bold'>(A) </span> 245 \qquad <span class='latex-bold'>(B) </span> 593 \qquad <span class='latex-bold'>(C) </span> 929 \qquad <span class='latex-bold'>(D) </span> 1331 \qquad <span class='latex-bold'>(E) </span> 1332