How to use simple algorithm for 4.2/28

How to use simple algorithm for 4.2/28

4.2÷28
＝4.2÷7÷4
＝0.6÷4
＝0.15

A simple algorithm of 40 × 1.28 × 40

= 40 X 40 X 1.28
= 1600 X 1.28
= 16 X 128
= 2^4 X 2^7
= 2^11
= 2048

17 and 34, 26 and 39, 48 and 56, 8 and 9, 1 and 100

17 and 34 17;
26 and 39 13;
48 and 562;
8 and 9 have no prime factor
1 and 100 have no quality factor
If you don't understand this question, you can ask,

Use a simple method to calculate the following questions 5.8 + 6.39 + 3.6113.56-1.48-3.5210.75
Use a simple method to calculate the following questions 5.8 + 6.39 + 3.6113.56-1.48-3.5210.75 + (0.4 + 2.25) 1.9 + 2.07 + 0.93 + 1.1

5.8+6.39+3.61
=5.8+(6.39+3.61 )
=5.8+10
=15.8
13.56-1.48-3.52
=13.56-(1.48+3.52)
=13.56-5
=8.56
10.75+( 0.4+2.25 )
=(10.75+2.25)+0.4
=13+0.4
=13.4
1.9+2.07+0.93+1.1
=(1.9+1.1)+(2.07+0.93)
=3+3
=6