marked price , discount and selling price

Find the Marked price.if selling price is=120 and discount =25%

ans: 

step 1: convert the discount into fractions= 25/100=1/4

step 2:  

           MP    -  discount =    SP

          4         -   1            =     3   (this is by the ratio that you got on step1)

  

(main logic behind is convert any problem into a fraction to solve it quickly. ie scale it down  )

now observer the ratio between actual  SP and ratio SP(step 2) 

120/3 =40  hence this ratio holds good for all other varying terms

therefore multiply 40 with 1( ratio profit)  =40

              multiply 40 with 4(ratio SP )       =4*40=160