GMAT OG2019 数学DS新题第277题(附解析)

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277. In a real estate office that employs n salespeople, f of them are females and x of the females are new employees. What is the value of n ?

(1) If an employee were randomly selected from the n employees, the probability of selecting a female would be 2/3

(2) If an employee were randomly selected from the f female employees, the probability of selecting a new employee would be 1/2

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. Each statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

词汇知识

randomly selected  随机选择

题目大意

在一家有n名销售人员的房地产公司,f名女性中新员工有x名。n的值是多少?

(1) 如果从n名员工中随机抽取一名员工,是女员工的概率为2/3

(2) 如果从f名女员工中随机挑选一名员工,是新员工的概率是1/2。

解题思路

(1) 知道随机抽取选取到女性的概率等于2/3,是可以求出n的值的,但是n有多个值,比如当n=3,f=2时;或n=6,f = 4时……随机抽取是女性的概率都是2/3。所以条件不充分;

(2) 从f名女员工中随机挑选道新员工的概率是1/2,无法求出n的值的,只能知道新员工占了女员工总人数的1/2,条件不充分。

(1)+(2),从条件1和条件2我们知道了两个关系,销售人员是女员工人数的3/2,新员工占女员工人数的1/2,但是因为所有的人数都是未知的,我们只知道比值的关系,所以符合条件的值有多个,值不唯一,条件不充分。

正确答案: E

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