9.8*2.7
=（10-0.2）*2.7
=27-0.54
=26.46
2003*2005-2002*2006
=(2002+1)(2006-1)-2002*2006
=-2002+2006-1
=3
2.3*2.4+0.23*53+23*0.23
=0.23*(24+53+23)
=0.23*100
=23
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