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?
- A.
Only S1 is correct
- B.
Only S2 is correct
- C.
Both S1 and S2 are correct
- 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

Both are irrational numbers.
But,

and 0 is rational.
Hence, S2 is also true.
Therefore, both S1 and S2 are correct.
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