Question 4
The price table shows that a pen costs 2 units and a ruler costs 1 unit. Consider these five invoices:
Invoice 1: 7 pens and 6 rulers
Invoice 2: 9 rulers and 5 pens
Invoice 3: 9 pens and 2 rulers
Invoice 4: 16 rulers and 2 pens
Invoice 5: 15 rulers and 2 pens
How many invoices have a total cost of 19 units?
Invoice 1: 7 pens and 6 rulers
Invoice 2: 9 rulers and 5 pens
Invoice 3: 9 pens and 2 rulers
Invoice 4: 16 rulers and 2 pens
Invoice 5: 15 rulers and 2 pens
How many invoices have a total cost of 19 units?