Here is a very good way to do approximations fast.

Hi,

We generally remember only a few convertions from fractions to percentages like 1/4 is 25% and
1/2 is 50 % like that. But in cases where we have to represent 45% in terms of percentages we put 45/100 and start simplifying.

Here is a very good way to make it simple with very little amount of data to remember.
With this we can easily convert percentages to fractions like,
How much is 3/17 (approximately) which is 17.4% and it takes no time.

How is this done?
Simple
3/17 is effectively 3*(1/17) now 1/17 value 5.8% and so 3/17 is 17.4.

How did you know that 1/17 is 5.8%? I have byhearted it!!

Here if we can byheart 1/2 to 1/20 then we can directly multiple with the values whatever we want,by this simplification needs very less steps.

In case any problem start like there is 45% profit we dont have to take number like 100 changed to 145 rather 17 changed to 20,which makes the simplifation easier.

Here is the list of all the fractions and its percentages from 1/2 to 1/20.

1/2  = 0.50 = 50%                                             1/11 = 0.09  = 9%
1/3  = 0.33 = 33%                                             1/12 = 0.083 =8.3%
1/4  = 0.25 =25%                                              1/13 = 0.076 =7.6%
1/5  =0.20  = 20%                                             1/14 =0.071 =7.1%
1/6  =0.16  =16%                                              1/15 =0.066 =6.6%
1/7  =0.14 =14%                                               1/16 =0.062 =6.2%
1/8  =0.12 =12%                                               1/17 =0.058 =5.8%
1/9  =0.11 =11%                                               1/18 =0.055 =5.5%
1/10 =0.10 =10%                                              1/19 =0.052 =5.2%
                                                                          1/20 =0.050 =5.0%

Cheers!