Question

简便计算：①2000乘2001分之2000 ②8分之3乘0.25加4分之1乘8分之5减4分之1

③20分之17乘3分之2加20分之17乘3分之1减2分之1 ④2008又2007分之1乘2008分之2007

Answer 1

2000 X ( 2000 /2001 )
= 2000 X ( 1 - 1/2001 )
= 2000 - 2000/2001
= 1999 + 1/2001

3/8 X 0.25 + 1/4 X 5/8 - 1/4
= 1/4 X 3/8 + 1/4 X 5/8 - 1/4
= 1/4 X ( 3/8 + 5/8 - 1 )
= 1/4 X ( 8/8 - 1 )
= 0

17/20 X 2/3 + 17/20 X 1/3 - 1/2
= 17/20 X ( 2/3 + 1/3 ) - 1/2
= 17/20 X 3/3 - 1/2
= 17/20 - 10/20
= 7/20

( 2008+ 1/2007 ) X ( 2007 /2008 )
= 2008 X 2007/2008 + 2007/2008 X 1/2007
= 2007 + 1/2008