A 68mm bottle of glue sells for $1.75. A larger 270mm bottle of the same glue sells for $7.35. Which is a better buy?

Question

A 68 mm bottle of hair dye sells for $1.75, a larger bottle of the same exact hair dye that is 270mm sells for $7.35. Which bottle of hair dye is the better buy? 

Answer 1

Unit cost of smaller one=1.75/68 dollars per mm=$0.0257/mm.

Unit cost of larger one=7.35/270=$0.0272/mm.

Therefore the smaller one is the better buy (cheaper).