Question

用简便方法计算下列各题（要有过程，脱式计算）

0.78×98

3.6×1.9+0.36×81
7.6×2.4+6.5×7.6+7.6+0.76

Answer 1

0.78×98
=0.78×（100-2）
=0.78×100-0.78×2
=78-1.56
=76.44

3.6×1.9+0.36×81
=3.6×1.9+3.6×8.1
=3.6×（1.9+8.1）
=3.6×10
=36

7.6×2.4+6.5×7.6+7.6+0.76
=7.6×（2.4+6.5+1+0.1）
=7.6×10
=76

Answer 2

0.78×98
=0.78×（100-2）
=0.78×100-0.78×2
=78-1.56
=76.44
3.6×1.9+0.36×81
=3.6×1.9+3.6×8.1
=3.6×（1.9+8.1）
=3.6×10
=36
7.6×2.4+6.5×7.6+7.6+0.76
=7.6×2.4+7.6×6.5+7.6×1+7.6×0.1
=7.6×（2.4+6.5+1+0.1）
=7.6×10
=76

Answer 3

4.8×0.25
=1.2×4×0.25
=1.2×1
=1.2

2.33×0.5×4
=2.33×2
=4.66

1.5×105
=1.5×(100+5)
=1.5×100+1.5×5
=150+7.5
=157.5

1.2×2.5＋0.8×2.5
=2.5×(1.2+0.8)
=2.5×2
=5