(b) Write \( \{x \in U \mid x \) is divisible by 5\( \} \) by listing the elements in braces. Choose the correct answer below. A. \( \{5,10,15,20\} \) B. \( \varnothing \) C. \( \{10,20\} \) D. \( \{1,2,3,4,6,7,8,9,11,12,13,14,16,17,18,19\} \)

To answer the question, we need to identify the elements in the universal set \( U \) that are divisible by 5. Typically, in a standard set for such problems, we can consider a range such as the first few positive integers. Looking at the provided options, option A \( \{5,10,15,20\} \) includes numbers that are clearly divisible by 5, while the others do not reflect that group accurately or represent numbers outside of that criterion. So, the correct choice is: A. \( \{5,10,15,20\} \) Now, onto some fun knowledge! You might be surprised to learn that the number 5 has often been considered a lucky number in various cultures! For instance, in Chinese culture, the number is associated with the five elements: wood, fire, earth, metal, and water. So, next time you see a number divisible by 5, think of how it might just bring you some good fortune! And when it comes to problem-solving, a common mistake is overlooking negative numbers or zero in your universal set. Always clarify your set boundaries! For instance, if your universal set is all integers, consider including negative multiples of 5 like -5, -10, etc., as they also fit the divisibility criterion. Keep your eyes peeled for those sneaky negatives!