lets say the large is 100 oz and cost 100$
assuming this:
Small contains 50 oz
Medium contains 80 oz
Small costs 35$
Medium costs 70$
so to buy large you get 1 oz per $1.00
to buy medium you get 1 oz per $1.14
to buy large you get 1 oz per $1.43
Therfore LMS is correct
