arithmetic sequence of 1/3,7/12,5/6
1/3=4/12
4/12+3/12=7/12
7/12+3/12=10/12=5/6
3/12=1/4
common difference is 1/4
first term is 1/3
an=a1+d(n-1)
an=1/3+(1/4)(n-1)
