In an effort to increase sales of spinach rolls, a vendor offered samples at a grocery store. The store sold an average of 10 boxes a day without offering samples. On the day the vendor offered samples, the store sold 25 boxes. What was the percent increase in sales of spinach rolls when samples were offered?

Answer 1

First find the difference in sales by subtracting the initial number of boxes sold from the final number: 25 boxes - 10 boxes = <<25-10=15>>15 boxes
Then divide that number by the initial number of boxes and multiply by 100% to find the percentage increase: 15 boxes / 10 boxes * 100% = 150%. Answer: \boxed{150}.