2×10+15
=20+15
=35
(143-24)×16
=119×16
=(120-1)×16
=120×16-1×16
=120×(10+6)-16
=120×10+120×6-16
=1200+720-16
=1200+704
=1904
3.4×2.3+0.7
=3.4×(2+0.3)+0.7
=3.4×2+3.4×0.3+0.7
=6.8+1.02+0.7
=8.52
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