Question:medium

A chose an integer X, which is between 2 and 40. A noticed that X is such a number that, when any integer Y is divided by X, the remainder is always 1. What is the value of X?

Show Hint

When solving modular arithmetic problems, always consider the largest prime number within the given range that satisfies the conditions. Primes are key to problems involving divisors and remainders
Updated On: Nov 26, 2025
  • 37
  • 41
  • 39
  • 41! + 1
Hide Solution

The Correct Option is A

Solution and Explanation

Problem Definition:

The integer \(X\) must satisfy the condition that for any integer \(Y\), the remainder of \(Y\) divided by \(X\) is always 1. This can be expressed as:

\[ Y \mod X = 1 \]

Properties of \(X\):

Given that \(X\) must be within the range of 2 to 40, it follows that \(X\) is not divisible by any integer from 2 to 40. Mathematically, \(X\) must be co-prime with all integers from 2 to 40.

Potential Values for \(X\):

The largest integer meeting this criterion is a prime number less than 40, which is not divisible by any number between 2 and 40. The largest prime number below 40 is 37.

Confirmation:

If \(X = 37\), then any integer \(Y\) divided by 37 will yield a remainder of 1:

\[ Y = k \cdot 37 + 1, \quad k \in \mathbb{Z}. \]

Therefore, \(X\) is determined to be 37.

Was this answer helpful?
0