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:

A subset's elements must all belong to its universal set. Set S contains letters (x, y), numbers (4, 9), and a symbol (?).

• U = {letters} only includes letters, so it cannot contain 4,9,?.
• U = {numbers} only includes numbers, so it cannot contain x,y,?.
• U = {punctuation marks} only includes punctuation, so it cannot contain x,y,4,9.
• U = {keys on a keyboard} includes letters, numbers, and symbols (like ?), so all elements of S fit in this set.

Answer:

U = {keys on a keyboard}