0.1+0.2+0.3+0.4+0.5+0.6.0.97+0.98+0.99
=（0.1＋0.2＋...＋0.9）＋（0.10＋0.11＋...＋0.99）
=（0.1＋0.9）×9÷2＋（0.10＋0.99）×90÷2
=4.5＋49.05
=53.55