A simple calculation method of 2.8 × 1.6 + 4.25.4 × 2.3-7.64 To say the reason to write complete Oh!

A simple calculation method of 2.8 × 1.6 + 4.25.4 × 2.3-7.64 To say the reason to write complete Oh!

2.8*1.6+4.2=（1.4*2）*1.6+1.4*3=1.4*（2*1.6+3）=1.4*6.2=1.4*（6+0.2）=1.4*6+1.4*0.2=8.4+0.28=8.687.64=5.4*1.65.4*2.3-7.64=5.4*2.3-5.4*1.6=5.4*（2.3-1.6）=5.4*0.7=3.78

(5 / 7) + (3 / 4) * (5 / 6) - (3 / 8) =? Simple algorithm
If there is no simple algorithm, please write it

（5/7）+（3/4）*（5/6）-（3/8）
=（5/7）+（5/8）-（3/8）
=（5/7）+（1/4)
=10/7

Simple algorithm of 2.85 * 3.8 + 4.6 * 2.85 + 8.4 * 7.15

2.85*3.8+4.6*2.85+8.4*7.15
=2.85*（3.8+4.6）+8.4*7.15
=2.85*8.4+8.4*7.15
=8.4*（2.85+7.15）
=8.4*10
=84