If the typical balance on lucy's credit card is $650 and the interest rate (apr) on her credit card is 18%, how much in interest would you expect lucy to be charged in a typical month?

Regular selling price (price before discount) 100%.

Price after trade discount of 15% is 85% of regular selling price..

Price after trade discount reduced to 10% is 90% of regular selling price.

By reducing the trade discount from 15% to 10% meant increasing the selling price by 5% of the selling price before applying the trade discount.