(1)(1/2-1/4+1/5)×20
=1/2×20-1/4×20+1/5×20
=10-5+4
=9
(2)71又16/15×(-8)
=(71+15/16)×(-8)
=71×(-8)+15/16×(-8)
=-568-15/2
=-568-7-1/2
=-(575+1/2)
=负575又1/2
(3)-12又1/9×9
=-(12+1/9)×9
=-12×9-1/9×9
=-108-1
=-109