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题库 / Prep2007E2-DS-207
At a certain theater, the cost of each adult's ticket is $5 and the cost of each child's ticket is $2. What was the average (arithmetic mean) cost of all the adults' and children's tickets sold at the theater yesterday?
(1) Yesterday the ratio of the number of children's tickets sold at the theater to the number of adults' tickets sold at the theater was 3 to 2.
(2) Yesterday 80 adults' tickets were sold at the theater.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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(1)Na/Nc=3/2, 能约掉
这道题条件一就可以，c/a=3/2， c=1.5A， 代入原式， a可以被约掉，直接可以求出平均值