小学分数应用题!!!!!!!!!!!!!!!!!!

快!!!
1.一次接力赛跑,小叶跑了全长1/5,小名跑了1/3,两人跑了400米.全长一共多少米?????

共长：400/（1/5+1/3）=750米

2.1/2*3+1/3*4+1/4*5+1/5*6=?

=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6

=1/2-1/6

=1/3

3.1/2001*2000+1/2001*2002+1/2002*2003+1/2003*2004

=1/2000-1/2001+1/2001-1/2002+1/2002-1/2003+1/2003-1/2004

=1/2000-1/2004

=4/2000*2004

=1/1002000

1.400/(1/5+1/3)=750米
2.1/2*3+1/3*4+1/4*5+1/5*6
=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)
=1/2-1/6
=1/3
3.1/2001*2000+1/2001*2002+1/2002+2003+1/2003+2004=?
应该是1/2001*2000+1/2001*2002+1/2002*2003+1/2003*2004=? 吧?
如果是1/2001*2000+1/2001*2002+1/2002*2003+1/20032004
就=1/2000-1/2004=1/1002000
如果没有错.那就是
1/2001*2000+1/2001*2002+1/2002+2003+1/2003+2004
=1/2000-1/2002+1/2002+1/2003+4007
=4007+4003/4006000

400除以（1/5+3/1)=750

1/1*2+1/2*3+1/3*4+1/4*5+1/5*6
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/