Perfume is sold in two different sizes of bottle. The 80 ml bottle is priced at £55.

The 50 ml bottle is usually priced at £45, but is on special offer.
If you buy one 50 ml bottle of perfume, you can get a second for half price.

By calculating the price per ml, determine which offers the best value for money,
the 80 ml bottle, or two 50 ml bottles?
You must show your working.