Q. यदि कोई दुकानदार अपनी लागत मूल्य से 50% अधिक माल की कीमत को चिह्नित करता है और 40% की छूट देता है, तो उसका लाभ या हानि प्रतिशत क्या है?

Explanation by: heera lal

suppose the real price is 100
then the shop keeper has 50% increse  so the  finalvalue is 100 + 50% of 100 
  then the value is 150 rupees 
then the shopkeeper has 40% discount to this value 
so 40% of the 150 rupees =40/100  * 150 =  60 
so the final price is 150 - 60 = 90 rupees 

real price is 100 but shopkeeper has sold the material have 90 rupees  
so the shopkeper has 10 rupees less