one day, Kwon's grocery store sold 70 bars of soap, some for $.85,some with a 25-cent off coupon for $.60. A total of $50 was taken in from the sale of bars of soap, but the cashier lost the coupons. How many bars of soap were sold with coupons?
—divine_Dei, December 08, 2001
This is a problem involving simultaneous equations. You have two unknowns and two equations to solve for them.