HP Printers vs. HP Ink Cartridges
You can buy an HP Deskjet 3747 color inkjet printer for $29.95. The printer includes a black HP 27 Black Inkjet Print Cartridge that sells separately for $18, and a HP 28 Tri-color Inkjet print cartridge that sells separately for $22. Therefore, it would be $10 cheaper to buy the printer ($30), and throw it out if you wanted the print cartridges for your current printer, compared to buying the print cartridges separately ($40)!
Reason: There are lots of substitutes for the HP Deskjet 3747 printer and consumers would be price sensitive (elastic demand) when shopping for the printer, but there are probably very few substitutes for the HP 27 and HP 28 print cartridges, and so once you have an HP printer that uses those print cartridges, you would be relatively price insensitive (inelastic demand) when buying the print cartridges.
Q: Why doesn't HP sell the 3747 printer at a price of at least the cost of the print cartridges sold separately, i.e. $40?