The Set S has "n" elements {x1,x1,...,xn}

Out of these "n" elements if we try to make subset of two element each then we can make 36 such subsets, which are correctly denoted by you as (a1,b1),(a2,b2),(a3,b3),(a4,b4)...............(a36,b36)

So, S' = (a1,b1),(a2,b2),(a3,b3),(a4,b4)...............(a36,b36)

(Note a ' after S in previous line)

Now, to find out the number of elements in the set S we are given by we can make 36 subsets of two elements each,

So number of subsets of two element each which can be formed from a Set S which has n elements = nC2

read the second half of the question which says "How many subsets of S could contain exactly three elements each"

So, S is the set of "n" elements and not the Set of subsets of two elements

Hope it helps!

paandey wrote:

Why nc2 = 36 ?

What I understand from question is that s = ((a1,b1),(a2,b2),(a3,b3),(a4,b4)...............(a36,b36))

Is this wrong understanding of question ? Kindly help

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Ankit

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