A shopkeeper marks his goods 30% above cost price. To be left with a profit of 4%, the discount he can allow on the marked price is what percent?

Take CP = 100, so MP = 130 and the required SP = 104. Discount = 130 − 104 = 26, but as a percent it must be taken on the marked price: 26/130 = 20%. (Reading 26 off the cost price is the usual slip.)