Let the number be x,100≤x≤999. (There are 900 three digits numbers)
A number divisible by both 2 and 3 must be divisible by the LCM of (2,3)=6.
Least value of x divisible by 6=102=6(17)
Greatest value of x divisible by 6=996=6(166)
There are 150 values of x divisible by 6 .
Required probability =900150=61