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}

Answer 1

U = {keys on a keyboard}

Explanation:

This is because x, y, 4, 9, ? are all keys located on a keyboard.

Answer 2

S is a subset of U, so all of the elements of S must be also elements of U

If U was {letters}, 4, 9, ? would not belong there
If U was {numbers }, x, y, ? would not belong to U
If U was {punctuation marks }, 4, 9, x, y would not be in U

all the elements of S are in U={ keys on a keyboard}

Answer: U={ keys on a keyboard}