Simple algorithm of 0.9 + 9.9 + 99.9

Simple algorithm of 0.9 + 9.9 + 99.9

0.9+9.9+99.9
=1-0.1+10-0.1+100-0.1
=1+10+100-3×0.1
=111-0.3
=110.7

How easy is it to divide (1 / 4 + 1 / 4 times 99) by 0.2

(1 / 4 + 1 / 4 times 99) divided by 0.2
=1/4*(1+99)/0.2
=0.25*100/0.2
=25/0.2
=125

5 / 7 x 11 / 12 x 4 fractional multiplication
Five out of seven x eleven out of twelve x four

5/7×11/12×4 =5/7×11/3 =55/21

Fractional multiplication: 4 × 4 / 3 = 10 / 7 × 24 = 9 × 12 / 5 = 8 / 3 × 8 = help, great Xia

4 × 3 / 4 = 3
7 / 10 × 24 = 16.8
9 × 5 / 12 = 3.75
3 / 8 × 8 = 3