Math Problem Statement

Solution

To solve the problem where we need to find the minimum possible value of a 3-digit number that, when divided by 7, 5, or 4, leaves a remainder of 2, we can approach it step by step.

Step 1: Understand the problem

We are asked to find a 3-digit number nn such that: n2(mod7),n2(mod5),n2(mod4)n \equiv 2 \pmod{7}, \quad n \equiv 2 \pmod{5}, \quad n \equiv 2 \pmod{4}

This means n2n - 2 must be divisible by 7, 5, and 4.

Step 2: Find the Least Common Multiple (LCM)

The number n2n - 2 should be a multiple of the LCM of 7, 5, and 4. First, we find the LCM:

LCM(7,5,4)=7×5×4=140\text{LCM}(7, 5, 4) = 7 \times 5 \times 4 = 140

So, n2=140kn - 2 = 140k for some integer kk, and thus: n=140k+2n = 140k + 2

Step 3: Find the minimum 3-digit nn

We now want to find the smallest kk such that n=140k+2n = 140k + 2 is a 3-digit number.

To do that, n100n \geq 100, so: 140k+2100140k + 2 \geq 100 140k98140k \geq 98 k981400.7k \geq \frac{98}{140} \approx 0.7 Since kk must be an integer, the smallest kk is k=1k = 1.

Step 4: Calculate nn

For k=1k = 1: n=140(1)+2=142n = 140(1) + 2 = 142

Therefore, the minimum possible value of nn is 142, which corresponds to option (C) 142.

Would you like more details or have any questions on this?


Here are 5 related questions you might find helpful:

  1. What would be the next possible 3-digit number after 142 that satisfies these conditions?
  2. How would you solve this problem using the Chinese Remainder Theorem?
  3. Can you generalize this method to any modulus, not just 7, 5, and 4?
  4. What if the remainder was 3 instead of 2, how would the solution change?
  5. How does the LCM affect the range of possible solutions?

Tip: Understanding the concept of modular arithmetic is key when dealing with divisibility and remainder problems.