## November 27, 2014

### 10th Class Maths Important Questions - New Syllabus - Sets Chapter for AP and Telangana

Q: Take any two sets of your choice to prove
i) AU B = B U A
ii) A ∩ B = B ∩ A.

Hint: As you are given choice to select two sets write any two sets A
and B and try to prove the relations. For example:
Solution: A = {1, 2, 3, 4, 5}
B = {3, 4, 5, 6, 7}
i) AU B = {1, 2, 3, 4, 5} U {3, 4, 5, 6, 7}
= {1, 2, 3, 4, 5, 6, 7}
BUA = {1, 2, 3, 4, 5, 6, 7}
A U B = B U A
ii) A ∩ B = {3, 4, 5}
B ∩ A = {3, 4, 5}
A ∩ B = B ∩ A

Q: From the given venn diagram, find
1) X U Y 3) X − Y
2) X ∩ Y 4) Y − X
What can you infer about X . Y, X n Y and X - Y?

Hint: Write the sets in roster form and answer the given questions. As
X Y, X - Y will be the empty set.
Solution: X = {2, 4}
Y = {1, 2, 3, 4, 5}
1) X . Y = {1, 2, 3, 4, 5} = Y
2) X n Y = {2, 4} = X
3) X - Y = {2, 4} - {1, 2, 3, 4, 5}= { }
4) Y - X = {1, 2, 3, 4, 5} - {2, 4} = {1, 3, 5}
X - Y is an empty set as X Y.

Q: Sneha has taken two sets of her choice and observed that n (A . B)
= n (A) + n (B). Jhansi argued that
n (A . B) = n (A) + n (B) - n (A n B). Who is correct? Give your reasons.

Hint: Jhansi's statement is correct for any two sets A and B. And
Sneha's statement is correct when the sets A and B are disjoint.
Solution: If the sets A and B are disjoint n (A n B) = 0
n (A . B) = n (A) + n(B)
This shows that Sneha has considered two disjoint sets.
But, for any two sets A and B
n (A . B) = n (A) + n (B) - n (A n B) is always true.
Jhansi's statement is true for any two sets A and B.
And Sneha's statement is conditionally true i.e., for only two disjoint sets.

Q: If n (A − B) = 10 and n (B − A) = 20 and n (A U B) = 45 then find n (A ∩ B).

Hint: This problem can be solved easily using a venn diagram.
Solution:
n (A U B) = n (A − B) + n (A ∩ B) + n (B − A)
45 = 10 + n (A ∩ B) + 20
n (A ∩ B) = 45 − 30 = 15

Q: Which of the following sets are infinite. Try to impose a condition
to make them finite.
i) A = {2, 4, 6, 8, ...}
ii) B = {a, e, i, o, u}
iii) C = {..., −3, −2, −1, 0, 1, 2, 3, ...}

Hint: You have many options to impose conditions to make the infinite
Sets A and C finite.
Solution:
Sets A and C are infinite sets as the elements of these sets are infinite.
i) A = {2, 4, 6, 8, ...}
The elements of Set A are multiples of 2. If the elements of Set A are
considered as the multiples of 2 less than 10 then it becomes finite.
ii) C = {..., −3, −2, −1, 0, 1, 2, 3, ....}
The elements of Set C are integers. If the elements of Set C are taken
as the integers that lie between −5 and 5 it becomes finite.