Question 1088604
Assuming everything costs the same, there are {{{4+5+3=12}}} choices, 4 are sandwiches.
{{{P=4/12=1/3}}}
.
.
The possible choices are 
{S,S}
{S,D}
{S,N}
{D,D}
{D,N}
{N,N}
and {S,D} is one of the possible choices.
{{{P=1/6}}}