递等式,怎样简便怎么算 0.98*302=?25*4.4*0.7=?5.8*5.8+5.8*0.5+5.8=?(0.25*12.5)*(4*0.8)=?

题目

递等式,怎样简便怎么算 0.98*302=?25*4.4*0.7=?5.8*5.8+5.8*0.5+5.8=?(0.25*12.5)*(4*0.8)=?
1.5*105=?32*1.25*2.5=?2.3+1.7*5.5=?

答案

0.98×302
=(1-0.02)×302
=1×302-0.02×302
=302-6.04
=295.96
25×4.4×0.7
=25×(4×1.1)×0.7
=(25×4)×(1.1×0.7)
=100×0.77
=77
5.8×5.8+5.8×0.5+5.8
=5.8×(5.8+0.5+1)
=5.8×7.3
=42.34
(0.25×12.5)×(4×0.8)
=(0.25×4)×(12.5×0.8)
=1×10
=10
1.5×105
=1.5×(100+5)
=1.5×100+1.5×5
=150+7.5
=157.5
32×1.25×2.5
=(8×4)×1.25×2.5
=(8×1.25)×(4×2.5)
=10×10
=100
2.3+1.7×5.5
=2.3+9.35
=11.65