secrets-of-mental-math-malestrom

Divide and Conquer: Mental Division 95
5 8 .625 (5 1 8 5 .125 .625) 6 8 3 4 .75
7 8 .875 (7 1 7 .125 .875)
8
The ninths have a magic all their own:
1 9 .1 2 9 .2 3 9 .3 4 9 .4
5 9 .5 6 9 .6 7 9 .7 8 9 .8
where the bar indicates that the decimal repeats. For instance,
4 9 .4 .444. . . . The tenths you already know:
1
2
3
.10 .20 .30
1 0
1 0
1 0
4
5
6
.40 .50 .60
1 0
1 0
1 0
7
8
9
.70 .80 .90
1 0
1 0
1 0
For the elevenths, if you remember that 1
11 .0909, the rest is
easy:
1
2
.09 .0909 ... .18 (2 .0909)
1 1
1 1
3
4
5
.27 (3 .0909) .36 .45
1 1
1 1
1 1