Roy wanted to get some pens and pencils. He went to a stationery shop that only sells them in boxes. A box of 7 pencils cost $2.50 while a box of 5 pens costs $3.20. Roy wants to buy 19 pencils and 3 pens. What is the least amount of money that he needs to spend on the pens and pencils?
19 pencils is 3 boxes of 7pencils (you have to pay for the extra 2 even though you do not want them)
3 pens is 1 boxes of 5 pens (you have to pay for the extra 2 even though you do not want them)
So Roy needs to buy 3 boxes of pencils and 1 box of pens. How much is that going to be?