A convenience store currently stocks 48 bottles of mineral water. The bottles have two sizes of either 20 or 40 ounces each. The average volume per bottle the store currently has in stock is 35 ounces. How many 40 ounce bottles must be sold for the average volume per bottle to be reduced to 25 ounces if no 20 ounce bottles are sold?
10
20
30
32
34
I'm having trouble understanding MGMAT explanation. I understand the calculations, but then the very last step it says:
"Since it would take 4 forty oz. bottles along with 12 twenty oz. bottles to yield an average volume of 25 oz, 36 - 4 = 32 forty oz. bottles must be sold.
The correct answer is D. "
The part in bold is where I get lost. Why would we subtract 4 when the work clearly shows 12 20 ounce bottle and 4 40 ounce bottles is the only combo that leads to an average of 25, yet the explanation says 12 20 ounce bottles and 32 40 ounce bottles?
There is something I clearly am not getting...