JAMB 2024 Mathematics · Question 4

Given that P is the set of all prime numbers between 0 and 10, and Q is the set of all odd numbers between 0…

Question

Given that P is the set of all prime numbers between 0 and 10, and Q is the set of all odd numbers between 0 and 10. Find the union of elements in P that are not in Q and the elements in Q that are not in P.

  1. A.{2, 9}
  2. B.{ 9}
  3. C.{1, 9}
  4. D.{1, 2, 9}

Answer: D. {1, 2, 9}

Explanation written with AI and checked against the answer key

Step 1: Analyze the Question

We are given two sets, PP and QQ, defined within the range of 0 to 10. We need to find the symmetric difference between these two sets, which is represented by the union of (P∖Q)(P \setminus Q) and (Q∖P)(Q \setminus P).

Step 2: Define the Sets
  • Set P (Prime numbers between 0 and 10): Prime numbers are numbers greater than 1 with only two factors (1 and itself). P={2,3,5,7}P = \{2, 3, 5, 7\}
  • Set Q (Odd numbers between 0 and 10): Odd numbers are integers not divisible by 2. Q={1,3,5,7,9}Q = \{1, 3, 5, 7, 9\}
Step 3: Solve Step-by-Step
  1. Find elements in P that are not in Q (P∖QP \setminus Q): These are prime numbers that are not odd. Looking at P={2,3,5,7}P = \{2, 3, 5, 7\} and Q={1,3,5,7,9}Q = \{1, 3, 5, 7, 9\}, the only element in PP that is not in QQ is 2. P∖Q={2}P \setminus Q = \{2\}
  1. Find elements in Q that are not in P (Q∖PQ \setminus P): These are odd numbers that are not prime. Looking at Q={1,3,5,7,9}Q = \{1, 3, 5, 7, 9\} and P={2,3,5,7}P = \{2, 3, 5, 7\}, the elements in QQ that are not in PP are 1 and 9. Q∖P={1,9}Q \setminus P = \{1, 9\}
  1. Find the union of these two results: Union means combining all unique elements from both sets. {2}∪{1,9}={1,2,9}\{2\} \cup \{1, 9\} = \{1, 2, 9\}
Step 4: Identify the Answer

Comparing our result {1,2,9}\{1, 2, 9\} to the given options, it matches option D.

Exam Tip

When dealing with set operations like "elements in P not in Q" (relative complement), always list your sets clearly first. Remember that 1 is not a prime number, which is a common trap in JAMB questions. Checking your set definitions carefully before performing the operation will save you from silly mistakes!

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