Answer :

- Apply the divisibility rule for 11: the difference between the sum of odd-placed digits and even-placed digits must be a multiple of 11.
- Let $x$ be the missing digit. Then $(1 + 2) - (7 + x)$ must be a multiple of 11.
- Simplify to get $-4 - x = 11k$ for some integer $k$.
- Solve for $x$ to find the missing digit: $x = 7$, so the missing digit is $\boxed{7}$.

### Explanation
1. Problem Analysis
We are given the number $172\square$ and we need to find the missing digit such that the number is divisible by 11. Let the missing digit be $x$. So the number is $172x$.

2. Divisibility Rule for 11
The divisibility rule for 11 states that a number is divisible by 11 if the difference between the sum of the digits in the odd places and the sum of the digits in the even places is either 0 or a multiple of 11.

3. Applying the Rule
Applying the divisibility rule to $172x$, we have $(1+2) - (7+x)$ must be divisible by 11. Simplifying this expression, we get $3 - (7+x) = 3 - 7 - x = -4 - x$.

4. Finding Possible Values
We need to find a digit $x$ such that $-4-x$ is divisible by 11. This means $-4-x$ can be $0, 11, -11, 22, -22$, and so on. Since $x$ is a digit, it must be between 0 and 9 inclusive.

5. Testing Values
If $-4-x = 0$, then $x = -4$, which is not a valid digit.
If $-4-x = 11$, then $x = -15$, which is not a valid digit.
If $-4-x = -11$, then $x = 7$, which is a valid digit.
If $-4-x = 22$, then $x = -26$, which is not a valid digit.
If $-4-x = -22$, then $x = 18$, which is not a valid digit.

6. The Missing Digit
The only valid digit we found is $x=7$. Therefore, the missing digit is 7.

7. Verification
The number is 1727. Let's check if it's divisible by 11: $1727 \div 11 = 157$. So, 1727 is divisible by 11.

8. Final Answer
Therefore, the missing digit is $\boxed{7}$.

### Examples
Understanding divisibility rules, like the one for 11, is useful in cryptography when encoding or decoding messages. For instance, ensuring that a key or a part of an encrypted message is divisible by 11 can serve as a check for errors during transmission or storage. This helps maintain the integrity of the data and ensures that the decryption process can proceed correctly.

Thanks for taking the time to read Work out the missing digit to make it divisible by 11 tex 172 tex. We hope the insights shared have been valuable and enhanced your understanding of the topic. Don�t hesitate to browse our website for more informative and engaging content!

Rewritten by : Barada