menu search
person

Let Ui = 1 Xfor i ∈ 50 = Ui = 1 for i ∈ n Yi = T, where each Xcontains 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 :

(1) 45 

(2) 15 

(3) 50 

(4) 30

thumb_up_alt 0 like thumb_down_alt 0 dislike
156 views

1 Answer

 
verified

Correct answer is 30 

EXplaination:

n(Xi) = 10. Ui = 1 Xi for i ∈ 50 = T,

n (T) = 500 each element of T belongs to exactly 20 elements of 

Xi = 500/20 = 25 distinct elements 

So 5n/6 = 25 

n = 30

thumb_up_alt 0 like thumb_down_alt 0 dislike
...