We are looking for 3-digit numbers with 2 of the digits equal to 6.
These numbers will be of the form,
x66
6x6
66x
where, in each case, x is a digit with a value of 0 to 5 and 7 to 9, a total of 9 different values
There will be 9 different values for x in each of the three cases, i.e. 27 in total.
There are 1001 different integers between 0 and 1000.
So the fraction of them that contain exactly 2 sixes is: 2.7%