原式=
5/26*1/4+5/26*2/5-1/12
=5/2*1/13*1/4+1/13-1/12
=1/13(5/8+1)-1/12
=1/13*13/8-1/12
=1/8-1/12
=(12-8)/12*8
=4/12*8
=1/24