Question

Write the following sets in Roster form:

C = {x : x is composite number and 5 ≤ x ≤ 21}

Answer 1

C = {x : x is composite number and 5 < x < 21}

5 ≤ x ≤ 21 means x = 5, 6, 7, 8, 9, 10 ......, 21

But we are given that x is a complete number

∴ x = 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21

∴ Roster form of the given set C = {6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21}

Note: Composite numbers : The natural numbers (greater than 1), which are not prime, are called composite numbers.