1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23 25, 27,29 if we add 3 numbers From this we get the answer 30

none of these numbers added equal 30

Explanation:

it is impossible to get 30 when you have three odd numbers

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form