(1)(-20)+(+3)-(-5)-(+7)
=-20+3+5-7
=-19;
(2)(38+16?34)×24
=9+4-18
=-5;
(3)(?3)2?(32)3×29?6÷|?23|
=9?278×29?6×32
=9?34?9=?34;
(4)(-1)2013×|-5|-4×(-3)-42
=(-1)×5-(-12)-16
=-5+12-16
=-9;
(5)2(2a2+9b)-(3a2+4b)
=4a2+18b-3a2-4b
=(4a2-3a2)+(18b-4b)
=a2+14b.
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