Here are all possible rolls of a pair of dice:

(1,1)  (1,2)   (1,3)  (1,4)   (1,5)  (1,6)
 
(2,1)  (2,2)   (2,3)  (2,4)   (2,5)  (2,6)
 
(3,1)  (3,2)   (3,3)  (3,4)   (3,5)  (3,6)
 
(4,1)  (4,2)   (4,3)  (4,4)   (4,5)  (4,6)
 
(5,1)  (5,2)   (5,3)  (5,4)   (5,5)  (5,6)
 
(6,1)  (6,2)   (6,3)  (6,4)   (6,5)  (6,6)



Since we are given that the sum is less than 7, we will 
remove from the sample space all the ones which have sum
of 7 or more, leaving only those that have the given 
property.

The reduced sample space consists of 15 rolls is this:

(1,1)  (1,2)   (1,3)  (1,4)   (1,5)  
 
(2,1)  (2,2)   (2,3)  (2,4)  
 
(3,1)  (3,2)   (3,3) 
 
(4,1)  (4,2)   
 
(5,1)  
 

And I'll now color the doubles red.

(1,1)  (1,2)   (1,3)  (1,4)   (1,5)  
 
(2,1)  (2,2)   (2,3)  (2,4)  
 
(3,1)  (3,2)   (3,3) 
 
(4,1)  (4,2)   
 
(5,1)

So 3 out of the 15 are doubles.  So the probability is 3/15,
which reduces to 1/5, to three decimal places is .200

Edwin