（10-7/55×1）＋（9-7/55×1）＋（8-7/55×1）＋.＋（1-7/55×1）
=10/55-7/55+9/55-7/55+8/55-7/55+.1/55-7/55
=【（10+1）×10÷2】/55-7/55*10
=55/55-70/55
=1-14/11
=-3/11