Question

s is a subset within a universal set, u. if s = {x, y, 4, 9,?}, which could describe u? u = {keys on a keyboard} u = {letters} u = {numbers} u = {punctuation marks}

Explanation:

To determine the universal set \( U \) that can contain the subset \( S=\{x, y, 4, 9,?\} \), we analyze each option:

• Option "U = {letters}": The set \( S \) contains numbers (4, 9) and a punctuation mark (?), so it can't be a subset of just letters.
• Option "U = {numbers}": The set \( S \) contains letters (x, y) and a punctuation mark (?), so it can't be a subset of just numbers.
• Option "U = {punctuation marks}": The set \( S \) contains letters (x, y) and numbers (4, 9), so it can't be a subset of just punctuation marks.
• Option "U = {keys on a keyboard}": A keyboard has letter keys (x, y), number keys (4, 9), and punctuation keys (?), so \( S \) can be a subset of the set of keyboard keys.

Answer:

A. \( U = \{\text{keys on a keyboard}\} \)