用简便方法计算 4.56÷12.5÷0.8 3.2×10.1 38×99+38 7/15÷5+8/15×1/5 1-0.

4.56÷12.5÷0.8
=4.56÷(12.5×0.8)
=4.56÷10
=0.456
3.2×10.1
=3.2×(10+0.1)
=32+0.32
=32.32
38×99+38
=38×(99+1)
=38×100
=3800
7/15÷5+8/15×1/5
=7/15×1/5+8/15×1/5
=(7/15+8/15)×1/5
=1×1/5
=1/5
1-0.225÷0.9-0.75
=1-0.25-0.75
=1-(0.25+0.75)
=1-1
=0
65×65/66
=(66-1)×65/66
=65-65/66
=64又1/66
2.5×3.2×12.5
=2.5×4×0.8×12.5
=10×10
=100
再问： 2.9+29.9+299.9+2999.9 写出这个我给你分
再答： 2.9+29.9+299.9+2999.9 =3-0.1+30-0.1+300-0.1+3000-0.1 =3333-4*0.1 =3332.6