脱式计算．（能简算的要简算）（1）1990×1999-1989×2000(2)425÷[(25+13)×911](3)567+345×566567×345+222(4)4-[3.75×(1.2-13)+34]．

Question

脱式计算．（能简算的要简算）
（1）1990×1999-1989×2000
(2)(4)/(25) ÷[((2)/(5) +(1)/(3) )×(9)/(11) ]
(3)(567+345×566)/(567×345+222)
(4)4-[3.75×(1.2-(1)/(3) )+(3)/(4) ] ．

Answer 1

（1）1990×1999-1989×2000
=1990×1999-1989×1999-1989
=1999×-1989
=1999-1989
=10
（2） (4)/(25) ÷[（ (2)/(5) +(1)/(3) ）× (9)/(11) ]

= (4)/(25) ÷[ (11)/(15) × (9)/(11) ]
= (4)/(25) × (5)/(3)
= (4)/(15)
（3） (567+345×566)/(567×345+222)
= (345+345×566+222)/(567×345+222)
= (567×345+222)/(567×345+222)
=1
（4）4-[3.75×（1.2- (1)/(3) ） +(3)/(4) ]
=4-[ (15)/(4) × (13)/(15) + (3)/(4) ]
=4-4
=0