Question

can any one answer it

Answer 1

?

Answer 2

there will be \[{P^7_3\over3!}=\frac{7!}{3!(7-3)!}=\frac{7\times6\times5}{3\times2}=35\]
number of sets
of these, how many have non-repeating pairs?

Answer 3

there is no repeating one

Answer 4

of these "3" element sets, how many are unique, in the sense that they do not have "2" common elements

Answer 5

okay