Question

a flower girl buys roses at Rs.4 for 5 roses and sells them at Rs.5 for 4 roses.Find her profit per cent.

Answer 1

first equal number of roses in both by lcm 

cp of 5 roses = Rs 4
then 
cp of 20 roses = Rs 16

sp of 4 roses = Rs 5
then
sp of 20 roses = Rs 25

profit = sp - cp
     =    =25 - 16
         =9

p% = p/cp *100
      =9/16*100
      =225/4