Aptitude test : percentage shortcuts and tricks

Aptitude shortcut
In this post I describe some of the tricks of percentage calculation . 
by a certain percent , we means that many hundredths thus , x percent means x hundredths written as x% 






Fraction value of percentage :

1/2 = 50 %                   1/3 = 33.33%                      1/4 = 25%                     1/5 = 20 % 
1/6 =16.67%                1/7 = 14.28%                          1/8 =12.5%                1/9 = 11.11

Note :these fraction value helps to minimize the calculation

Formula:

  1. if the price of a commodity increases by R% , then the reduction in consumption so as not to increase the expenditure is 100*R/(100+R)%.
  2. if the price of a commodity decreases by R% , then the increases  n consumption so as not to decreases the expenditure is 100*R/(100-R)%.
  3. value of machine after n years = p(1-R/100)power n .
  4. if A is R% more than B , then b is less than A by 100*R/(100+R)%.
  5. if A is R% less than B , then b is more than A by 100*R/(100-R)%.

Example:

1. if 1/5 of a number is 25 less then 1/4 of a same number . what will be 3/2 of number .
ans.
                         as you know 1/5 = 20% and 1/4 = 25%
                         so difference b/w these two is 5% which is equal to 25 
                         then  5% *20  ---- 25*20     100% ----500
                        and 100% percent is the real value 
                        you can now calculate 3/2 so ans is    750

2. if the numerator of fraction is increase by 20% and denominator is decrease by 80% then fraction becomes 18/15. what is the actual fraction .

ans .                     120% N/20% D = 18/15
                             then N/D = (18/15 )*20/120
                             N/D = 1/5   answer

3 . if A's salary 20% less then B's salary then B's salary is how much more then A.

ans .                suppose B's salary is 100 then A's salary is 80
                        now you can calculate b's salary in respect to A
                      ( 20/80)* 100 = 25% is answer

4. A number is increased by 12% and again deceased by 18% then how much change in that value.

                   formula for this problem % change = (x)+(y)+x*y/100

Note take the value with symbol , if increase then take '"plus" if decease in value then take "minus". this formula is applicable for circle , square , triangle etc

                    12- 18 - 216/100 =   -8.16  decrease is value by 8.16% 



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