Which is the best buy?
A. $12.40 for 6 boxes of tissues
B. $10.58 for 5 boxes of tissues
C. $14.11 for 9 boxes of tissues
D. $15.47 for 8 boxes of tissues
12.4/6 = 2.06
10.58/5 = 2.12
14.11/9 = 1.57
15.47/8 = worse than 1.57
so
C is the minimum unit price per box