JAMB 2016 Mathematics · Question 34

Given U = {x: x is a positive integer less than 15} and P = {x: x is even number from 1 to 14}. Find the compliment of P.

Options

  1. A.{1, 3, 5, 7, 9, 11, 13, 15}
  2. B.{2, 3, 5, 7, 9, 11, 13}
  3. C.{1, 3, 5, 7, 9, 11, 13}
  4. D.{2, 3, 5, 7, 11, 15}

Answer: C. {1, 3, 5, 7, 9, 11, 13}

Explanation written with AI and checked against the answer key

1. Analyze the question

We are given a Universal set (UU) containing positive integers less than 15, and a subset (PP) containing even numbers from 1 to 14. We need to find the complement of PP (denoted as P′P' or PcP^c), which consists of all elements in UU that are not in PP.

2. Explain the concept
  • Universal Set (UU): The set of all elements under consideration. Here, "positive integers less than 15" means {1,2,3,4,5,6,7,8,9,10,11,12,13,14}\{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14\}.
  • Subset (PP): The set of even numbers from 1 to 14. These are {2,4,6,8,10,12,14}\{2, 4, 6, 8, 10, 12, 14\}.
  • Complement (P′P'): This is the set of elements that are in UU but are not in PP. Essentially, you remove all even numbers from the universal set, which leaves you with the odd numbers.
3. Show the solution
  • Step 1: List the elements of UU U={1,2,3,4,5,6,7,8,9,10,11,12,13,14}U = \{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14\}
  • Step 2: List the elements of PP P={2,4,6,8,10,12,14}P = \{2, 4, 6, 8, 10, 12, 14\}
  • Step 3: Find P′P' (Elements in UU not in PP) We remove {2,4,6,8,10,12,14}\{2, 4, 6, 8, 10, 12, 14\} from UU: P′={1,3,5,7,9,11,13}P' = \{1, 3, 5, 7, 9, 11, 13\}
4. Identify the answer

Comparing our result {1,3,5,7,9,11,13}\{1, 3, 5, 7, 9, 11, 13\} with the given options:

  • Option A includes 15 (which is not in UU because UU is less than 15).
  • Option B includes 2 (which is in PP).
  • Option C matches our result exactly.
  • Option D is missing several odd numbers.
5. Tip

When dealing with set complements, always double-check the definition of your Universal set. If the question says "less than 15," 15 is excluded. If it says "15 or less," 15 is included. Always list out the elements of the Universal set first to avoid missing numbers!

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