If a shopkeeper accidentally sells a pen at double its actual selling price, his profit increases 4 fold. Then he realizes his mistake and sells other pens at their original selling price. Find his actual profit percentage.

• let the original selling price be sp and the cost price be cp.
  
  If he sells the pen at double the selling price, his new profit will be 2sp - cp.
  His actual profit should had been (sp - cp). But his accidental rising of the selling price resulted in a four fold increase of the original profit which is 4 X (sp - cp).
  
  Hence, 2sp - cp = 4 X (sp - cp)
  Therefore sp = (3/2)cp.
  
  Actual profit percentage = (sp - cp)/cp % = 50%
• 12 years agoHelpfull: Yes(16) No(2)