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The universal set, $U = \{ 1, 2, 3, 4, 5, 7, 10, 11, 13, 17, 19, 20 \}$ - Junior Cycle Mathematics - Question 6 - 2012

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Question 6

The-universal-set,-$U-=-\{-1,-2,-3,-4,-5,-7,-10,-11,-13,-17,-19,-20-\}$-Junior Cycle Mathematics-Question 6-2012.png

The universal set, $U = \{ 1, 2, 3, 4, 5, 7, 10, 11, 13, 17, 19, 20 \}$. A is the set of prime numbers between 1 and 20. B is the set of factors of 20. (a) Lis... show full transcript

Worked Solution & Example Answer:The universal set, $U = \{ 1, 2, 3, 4, 5, 7, 10, 11, 13, 17, 19, 20 \}$ - Junior Cycle Mathematics - Question 6 - 2012

Step 1

List the elements of the set A.

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Answer

The elements of set A (the prime numbers between 1 and 20) are:

  • 2
  • 3
  • 5
  • 7
  • 11
  • 13
  • 17
  • 19

Step 2

List the elements of the set B.

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Answer

The elements in set B (the factors of 20) are:

  • 1
  • 2
  • 4
  • 5
  • 10
  • 20

Step 3

Fill in the Venn diagram below placing all elements of U in the correct regions.

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Answer

In the Venn diagram, the regions contain the following:

  • Set A (left circle): 2, 3, 5, 7, 11, 13, 17, 19
  • Set B (right circle): 1, 2, 4, 5, 10, 20
  • Intersection (A ∩ B): 2, 5
  • Unique to U: 16 not included in A or B.

Step 4

List the elements of A ∩ B.

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Answer

The elements of the intersection A ∩ B, which are in both sets A and B, are:

  • 2
  • 5

Step 5

Complete the sentence below.

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Answer

If an element is in the region A ∩ B, it has two properties: it is a prime number and it is a factor of 20.

Step 6

Explain where to place the number 16.

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Answer

The number 16 is added to the universal set. It is placed outside the circles representing sets A and B, as follows:

  • It is in U but not prime and is not a factor of 20.

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