There are 36 possible rolls and only one is a double 6, so the
probability of one double 6 in 1 roll is 1/36.
on your TI-84
press 2ND VARS
Scroll down to binompdf(, press ENTER
Don't get binompdf( and binomcdf mixed up, the "c" is for
"cumulative" and the "p" is for "particular value". This is
a particular number of times, 2.
trials:20
p:1/36
x value:2
Paste
Press ENTER
binompdf(20,1/36,2)
Press ENTER
.0882934291
Edwin