Skip to content / Đến nội dung
ThichHocToan.com

2020 AMC 12A Question 25

AMC12 · 2020 AMC 12A

Question 25

The number $a = \dfrac{p}{q},$ where $p$ and $q$ are relatively prime positive integers, has the property that the sum of all real numbers $x$ satisfying $$
\lfloor x \rfloor \cdot \{x\} = a \cdot x^2
$$ is $420,$ where $\lfloor x \rfloor$ denotes the greatest integer less than or equal to $x$ and $\{x\} = x - \lfloor x \rfloor$ denotes the fractional part of $x.$ What is $p + q?$
  1. $245$
  2. $593$
  3. $929$
  4. $1331$
  5. $1332$