19.8×7.8—24×5.3＋8.4×3.9
=19.8*7.8-24*5.3+4.2*2*3.9
=7.8(19.8+4.2)-24*5.3
=7.8*24-24*5.3
=24*(7.8-5.3)
=24*2.5
=2.5*20+2.5*4
=60
下面的看不懂
2006＋20062006
2008×———————
2008＋20082008