Because it is already there in the list of 280. Have a look at 237th
record 1-6-8 & 2-4-9 & 3-5-7

The basic idea is that there should be 3 combinations of 3 numbers each
and all the 9 basic numbers should be covered.

The formula that I discoved is as follows but I am not sure if this is
mathematically correct.

Basic numbers : 9
Combinations: 3

9/3=3 (there should be three steps to arrive to the final answer)

step1:

=combin(basic numbers,combination)/3
=combin(9,3)/3
=84/3=28

step2:
=combin(basic numbers - 3,combinations)/2
=combin(6,3)/2
=20/2=10

step3:
=combin(basic numbers - 6,combinations)/1
=combin(3,3)/1
=1/1=1

step1 answer x step2 answer x step3 answer

28*10*1=280


Tom Ogilvy wrote:
Why isn't
1-6-8 & 3-5-7 & 2-4-9 a legal combination.