Question

A shopkeeper declares a 20% discount on his goods and sell it at a profit of 25%. What is the cost price of the goods if the marked price quoted is Rs. 2000?

Answer 1

20% discount means you pay 80% of the marked price 
discounted price = 0.80·$2000 = $1600 

profit = discounted price - cost 
(discounted price - cost)/cost = profit as a percentage of cost 
($1600 - cost)/cost = 0.25 
$1600 - cost = 0.25·cost 
$1600 = 1.25·cost 
cost = $1600/1.25 = $1280