Q Consider the following statements: S1 ​: There exists infinite sets A,B,C…

2001

Q Consider the following statements:

S1 ​: There exists infinite sets A,B,C such that A∩(B∪C) is finite.

S2 ​: There exists two irrational numbers x and y such that (x + y) is rational.

Which of the following is true about S1​ and S2​?

  1. A.

    Only S1 is correct

  2. B.

    Only S2 is correct

  3. C.

    Both S1 and S2 are correct

  4. D.

    None of S1 and S2 is correct

Attempted by 104 students.

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Correct answer: C

Statement S1​:

There exist infinite sets A,B,C such that A∩(B∪C) is finite.

Example:

Let

A={1,2,3,… }

B={2,4,6,… }

C={−1,−2,−3,… }

Then A,B,C are infinite sets.

Now,

B∪C

contains positive even integers and negative integers.

Thus,

A∩(B∪C)={2,4,6,… } which is infinite.

But we can choose disjoint infinite sets:

Let

A={1,2,3,… }

B={−1,−2,−3,… }

C={−10,−11,−12,… }

Then,

A∩(B∪C)=∅ which is finite. Hence, S1 is true.

Statement S2:

Take

image.png

Both are irrational numbers.

But,

image.png

and 0 is rational.

Hence, S2​ is also true.

Therefore, both S1​ and S2​ are correct.

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