GMAT OG2019 数学DS新题第248题(附解析)

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248. Last semester, Professor K taught two classes, A and B. Each student in class A handed in 7 assignments, and each student in class B handed in 5 assignments. How many students were in class A ?

(1) The students in both classes combined handed in a total of 85 assignments.

(2) There were 10 students in class B.

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.

题目大意

上学期K教授教了A和B两个班,A班每个学生交了7本作业,B班每个学生交了5本作业。A班有多少学生?

(1) 两个班学生总共交了85本作业。

(2) B班有10名学生。

解题思路

(1) 两班学生共交85本作业,却无法得知A班交了多少作业,有多少学生,条件不充分;

(2) B班有10名学生,却无法得知A班有多少学生,条件不充分;

(1)+(2),B班有10名学生,每名学生交5本作业,所以B班学生共交10×5=50本作业。A班学生共交作业85 - 50 = 35本,每名学生交7本作业,所以A班有35÷7= 5名学生。值唯一,条件充分。

正确答案: C

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