一道SAT数学题.
if 4 bags of flour with an average weight of 15 pounds are put onto a shelf with 45-pound bags of flour,what is the average weight,in pounds,of all 8bags on the shelf?
(A)5
(B)10
(C)15
(D)20
(E)25
答案是10,但我怎么算都不是10...不知道是我没看懂题还是.....