In a Δ sum of two sides should be greater then the third side
It is given that Δ is isosceles
∴ Total cases in which isosceles Δ will come is
(1,1,1),(2,2,3),(2,2,1),(2,2,2),(3,3,4),(3,3,1),(3,3,2),(3,3,3),(3,3,5),(4,4,1),(4,4,2),(4,4,3),(4,4,4),(4,4,5),(4,4,6),(5,5,1),(5,5,2),(5,5,3),(5,5,4),(5,5,5),(5,5,6),(6,6,1),(6,6,2),(6,6,3),(6,6,4),(6,6,5),(6,6,6)
Total cases =27×3−12=69
Favorable cases =1
Probability = 691.