I believe that the following represents the intent of the problem:
AAPL wrote:A boy is buying two kinds of marbles. One kind costs 25 cents per pound and he purchased 5 pounds of this kind. The other kind of marble costs 32 cents per pound. The boy purchases x pounds of the more expensive marble, where x is an integer. If the average cost per pound for the boy's entire purchase must be as close as possible to 29 cents, what is the value of x?
A. 5
B. 6
C. 7
D. 8
E. 9
Cost of 5 pounds of 25-cent marbles = 5*25 = 125 cents.
We can PLUG IN THE ANSWERS, which represent the number pounds of 32-cent marbles.
When the correct answer is plugged in the average cost per marble ≈ 29.
B: 6 pounds of 32-cent marbles, for a total of 11 pounds of marbles
Average cost for the 11 pounds of marbles = (125 + 6*32)/11 = 28.8.
The average cost is just under 29 cents.
Test whether C yields an average cost closer to 29 cents,
C: 7 pounds of 32-cent marbles, for a total of 12 pounds of marbles
Average cost for the 12 pounds of marbles = (125 + 7*32)/12 = 29.08.
Since C yields an average cost closer to 29 cents than does B, eliminate B.
The correct answer is
C.
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