WAEC 2013 Mathematics · Question 30
If p = (y : 2y 6) and Q = (y : y -3 4), where y is an integer, find pQ
Options
- A.{3, 4}
- B.{3, 7}
- C.{3, 4, 5, 6, 7}
- D.{4, 5, 6}
Answer: C. {3, 4, 5, 6, 7}
Explanation written with AI and checked against the answer key
Step 1: Analyze the question We need the intersection of two sets of integers, P and Q. The intersection contains only the values that satisfy both conditions.
Step 2: Solve each inequality
- P: 2y ≥ 6, so y ≥ 3
- Q: y − 3 ≤ 4, so y ≤ 7
Step 3: Find the intersection P ∩ Q contains the integers with 3 ≤ y ≤ 7:
P ∩ Q = {3, 4, 5, 6, 7}
Step 4: Check against the options
- A {3, 4}: too few elements
- B {3, 7}: leaves out 4, 5 and 6
- C {3, 4, 5, 6, 7}: matches our result
- D {4, 5, 6}: wrongly excludes the end values 3 and 7
Both inequalities include "equal to" (≥ and ≤), so the end values 3 and 7 are part of the set.
Exam tip: When you see ≥ or ≤, include the boundary values. Whenever the signs are > or <, leave them out. For intersection questions, first write each set as a range, then pick the overlap, which here is 3 ≤ y ≤ 7.
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