CMA Foundation · Fundamentals of Business Mathematics and Statistics · Set Theory, including Venn Diagram
The set A is defined in roster form as A = {x : x is a natural number, 3 < x ≤ 12 and x is divisible by 3}. What is the sum of all elements of A?
The sum is 27. The set contains the natural numbers above 3 and up to 12 that are multiples of 3, namely 6, 9 and 12. Adding these gives 27. Including 3 or excluding 12 would give wrong totals.
- A18
- B27Correct
- C30
- D21
Explanation
Natural numbers greater than 3 and up to 12 that are divisible by 3 are 6, 9 and 12. Their sum is 6 + 9 + 12 = 27. The value 18 comes from leaving out 12, and 30 comes from wrongly including 3.
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