Probability

Three distinct numbers are selected randomly from the set {1, 2, 3, . ..,40}.

If the probability, that the selected numbers are in an increasing G.P, is m/n

gcd(m, n) = 1, then m + n is equal to?

will we have to list out all the possibilities? is there like a standard thing where i dont miss a case because i only considered

1,2,4,8...

1,3...

1,4...

1,5...

basically all 1 sei start hone valei