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一、Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?

(1) She bought $4.40 worth of stamps.

(2) She bought an equal number of $0.15 stamps and $0.29 stamps.

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 statement TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D EACH statement ALONE is sufficient.

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

正确答案：

A

题目分析：

Joanna只买了0.15和0.29两种价值的邮票，问她买了多少枚0.15的邮票?

单独看条件1：总共买了价值4.4的邮票。这道题隐含着一个条件：邮票数是正整数。因为4.4分成正整数的0.29与0.15组合只有一种情况，也就是各买了10枚。所以是唯一解，条件1自己就可以满足。

单独看条件2：两种邮票买了一样的数量。没有总价，没有上限，无法从条件2单独得出结果。所以条件2 not sufficient.

根据以上结论，得出答案为A。

二、The figure shown represents a board with 4 rows of pegs, and at the bottom of the board are 4 cells numbered 1 to 4. Whenever the ball shown passes through the opening between two adjacent pegs in the same row, it will hit the peg directly beneath the opening. The ball then has the probability 1/2 of passing through the opening immediately to the left of that peg and probability 1/2 of passing through the opening immediately to the right. What is the probability that when the ball passes through the first two pegs at the top it will end in Cell 2?

正确答案：

D

题目翻译：

如果一个球穿过某一行某两个桩中间的空间，那它一定会碰到下一行的那个桩,而每碰到一次，球往左和往右走的概率都是50%，现在有一个球掉进了最上面那行的两个桩中间，请问落进最下面一行第2和第3个桩之间的“Cell2”的概率。

解题思路：

把概率累加一下就可以了。第二行就是50%/50%。第三行是25%/50%/25%。那最后一行就是12.5%/37.5%/37.5%/12.5%。所以掉进Cell2的几率是37.5%，也就是D选项。

三、If n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24, what is the value of r?

(1) 2 is not a factor of n.

(2) 3 is not a factor of n.

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 statement TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D EACH statement ALONE is sufficient.

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

正确答案：C

解题思路：

从条件1看，2不是n的约数，也就是说n是奇数，所以n+1和n-1都是偶数。

令n=1，代入(n-1)(n+1)/24得到余数为0

令n=3，代入(n-1)(n+1)/24得到余数为8

令n=5，代入(n-1)(n+1)/24得到余数为0

结果不唯一，所以不充分。

同理，条件2之下我们也可以代数来算：

令n=1，代入(n-1)(n+1)/24得到余数是0

令n=2，代入(n-1)(n+1)/24得到余数是3

令n=4，代入(n-1)(n+1)/24得到余数是15

结果亦不唯一，所以也不充分。

然后1+2，也就是说n是不能被3整除的奇数：

令n=1，代入(n-1)(n+1)/24得余数为0

令n=5，代入(n-1)(n+1)/24得余数为0

令n=7，代入(n-1)(n+1)/24得余数为0

...

结果唯一，所以1+2充分，选择C。

好了，以上就是2020年GMAT考试《GMAT数学》每日一练（10）的全部内容了，如果各位小伙伴还有不明白的地方，可以进入帮考网咨询了解哦！