Topic Question Set


Q 21 :

Let ∪i=150Xi=∪i=1nYi=T, where each Xi contains 10 elements and each Yi contains 5 elements. If each element of the set T is an element of exactly 20 of sets Xi's and exactly 6 of sets Yi's, then n is equal to

  • 15

     

  • 50

     

  • 45

     

  • 30

     

(4)

∪i=150Xi=∪i=150Yi=T    

∵    n(Xi)=10, n(Yi)=5

So, ∪i=150Xi=500,    ∪i=150Yi=5n

⇒50020=5n6

⇒n=30



Q 22 :

Let set A={x∈I+:f(x)=x3-8x2+20x-13 is a prime number}. Consider the statements:

Statement – I: Number of elements in set A is 3

Statement – II: Sum of all elements in set A is 9, then

  • Both Statement – I and Statement – II are true

     

  • Statement – I is true and Statement – II is false

     

  • Statement – I is false and Statement – II is true

     

  • Both Statement – I and Statement – II are false

     

(1)

A={2,3,4}



Q 23 :

Each student in a class of 40, studies at least one of the subjects English, Mathematics and Economics. 16 study English, 22 Economics and 26 Mathematics, 5 study English and Economic, 14 Mathematics and Economics and 2 study all the three subjects. Then the number of students who study English and Mathematics but not Economics is

  • 7

     

  • 5

     

  • 10

     

  • 4

     

(2)

n(A∪B∪C)=16+22+6-5-14-K+2⇒40=47-K⇒K=7

⇒ Number of students who study English and Mathematics but not economics=5