(1).999*1999
=(1000-1)*1999
=1999000-1999
=1997001
(2) (1/15+2/17)*15*17
=17+2*15
=47
(3) 20000/12.5/25/0.8/4
=20000/(12.5*0.8*25*4)
=20000/(10*100)
=20000/1000
=20
(4) 38*1/4+17*0.25+45*25%
=38*1/4+17*1/4+45*1/4
=(38+17+45)*1/4
=100*1/4
=25