桂林北到桂林西打的:数学问题

3.
998*13*77
=(1000-2)*13*77
=1000*221-2*221
=221000-442
=220558
4.
2001*485/29+2001*1545/87
=2001*1455/87+2001*1545/87
=2001*(1455+1545)/87
=3000*2001/87
=3000*23
=69000
5.
1999*2001*4000001
=(2000-1)(2000+1)(4000000+1)
=(4000000-1)(4000000+1)
=16000000000000-1
=15999999999999
6.
9999*9999*19999
=(10000-1)(10000-1)(20000-1)
=(100000000-20000-1)(20000-1)
=2000000000000-100000000-400000000-40000+1
=1999499960001
7.
71*0.47+0.65*14.7-0.521*4.7
=7.1*4.7+0.65*10+0.65*4.7-0.521*4.7
=4.7(7.1+0.65-0.521)+6.5
=4.7*7.229+6.5
=40.4763
8.
(393939*899899)/(377377*939393)
=(131313*899899)/(377377*313131)
=(43771*899899)/(377377*104377)
=(43371*2387)/(1001*104377)
=(6253*2387)/(143*104377)
=(6253*341)/(143*14911)
=(481*341)/(143*1147)
=164021/164021
=1
9.
2001－2000－1999＋1998＋1997－1996＋1995－1994－1993＋1992＋ 1991－1990＋……+9－8 －7＋6＋5－4＋3－2－1
=[(2001-3)/6]*1
=333
10.
20002001*20012000-20002000*20012001
=20002000(20012000-20012001)+20012000
=-20002000+20012000
=10000