The #n^"th"# term, #a_n# of an arithmetic sequence, with initial term, #a_1# and incremental difference #d# is given by the formula: #color(white)("XXX")a_n=a_1+(n-1)*d#
In this case with #n=12, a_1=5, " and " d=1/3# #color(white)("XXX")a_12=5+(12-1)*1/3=5+11/3=8 2/3#