Skip to content / Đến nội dung
ThichHocToan.com

ITMC 2026 Grade 8 National Preliminary sample-r1 Question 14

ITMC · ITMC 2026 Grade 8 National Preliminary sample-r1

Question 14

For real $x$, $[x]$ denotes the greatest integer not exceeding $x$ (the integer part). The decimal or fractional part is $\{x\}=x-[x]$, so $x=[x]+\{x\}$. Examples: $[3]=3$, $[6.25]=6$, $[-6.25]=-7$, $[22/7]=3$. The source lists: (1) $0\lt \{x\}\lt 1$ for every real $x$; (2) $\{x\}=0$ exactly when $x$ is an integer; (3) $x-1\lt [x]\le x\lt [x]+1$; (4) $[n+x]=n+[x]$ for positive integers $n$; (5) $[-x]=-[x]-1$ if $x$ is not an integer, and $[-x]=-[x]$ if $x$ is an integer. Editorial correction: property (1) must read $0\le\{x\}\lt 1$; its printed strict lower bound contradicts (2). The definition of $[x]$ is used below.

For positive integers $n$ satisfying $[\sqrt n]=5$, find the sum of all possible $n$.
  1. 281
  2. 305
  3. 330
  4. 366
  5. None of these.