First bottle unit cost: 80/55=16/11 pounds per ml
Second deal, buy 50ml for 45pounds and get one more at half price, unit cost of
(50 + 50) / (45 + 45/2) = 40/27 pounds per ml
Which is bigger? Let's try without the calculator.
16/11 - 40/27 = ( 16(27)-11(40) ) / 287= (432 - 440) / 287 < 0
16/11 is a smaller unit cost.
Answer: 80 ml bottle is a better value
