a shopkeeper bought potatoes at the rate of rs 500 per 100 kg and sold them at the

 20%

Step-by-step explanation:

if 500 = 100kg

          = 10kg

     50 = 10kg

%Profit = S.P/B.P *100

%Profit = 60/50 *100

%Profit = 120%

%Profit = 120% -100% = 20%

Well I don't know !
Let's find it together:

The factors of  12  are  1,  2,  3,  4,  6,  and  12 .

The factors of  20  are  1,  2,  4,  5,  10,  and  20 .

The factors of  36  are  1,  2,  3,  4,  6,  9,  12,  18,  and  36 .

The common factors of  12,  20,  and  36 (the ones that
show up on all three lists) are ...

                       1,  2, and  4 . 

The greatest one of these is  4 .