数学几问

Q10:

A set of numbers has the property that for any number t in the set, t + 2 is in the set.  If –1 is in the set, which of the following must also be in the set?

I.                    -3

II.                 1

III.               5

A.    I only

B.    II only

C.    I and II only

D.    II and III only

E.    I, II, and III

A.        0

B.        1/9

C.        2/9

D.       1/3

E.        1

1，－1在，所以－1＋2＝1在，－1＋n2都在

所以选（2）（3）

2，三辆车排序又P3，3

随便坐有3×3×3种

所以几率是P3，3/3^3

法二：

第一次随便坐哪个车，第二次有2/3的机会不坐同一个车，第三次有1/3的机会

嗯,第一题还是有点没想明白,还是没明白为什么-3不在

既然T,T+2都是数列内的,如果T+2是-1的位置时,那么T不就是-3,为什么-3不在数列中呢,请NN指教

还有一题,麻烦版主解答

A total of $60,000 was invested for one year.  But of this amount earned simple annual interest at the rate of x percent per year, and the rest earned simple annual interest at the rate of y percent per year.  If the total interest earned by the $60,000 for that year was $4,080, what is the value of x?

(1)     x = (3/4) y

(2)   The ratio of the amount that earned interest at the rate of x percent per year to the amount that earned interest at the rate of y percent per year was 3 to 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.

这个基本上没太看明白,欢迎高人指点迷津^

lz你是想反了的

人家说如果有t，就有t+2；那现在告诉你有-1，你自然应该假设-1为t了，而不是假设其为t+2

哦,那反过来想就是不可以的了,这种题都是这种思路的吗

还有那道看不懂的题麻烦高手再解答下.谢谢~~~

实际偶阅读很烂的，也没太读懂，但是大意可以明白。

就是有个哥们特有钱，有60，000这么多钱，然后他要投资。结果就一分为二去存款了，其中一部分的存款(假设为C)利息是x，另一部分的利息是y，然后他投了一年，利息一共有4080块，问你x是多少？

那么根据条件2可知：C/60000-c=3/2 我们就知道了C是多少，也就是两部分的本金都是多少。

然后列式子 Cx+(60000-C)y=4080

再根据条件1，x=(3/4)y

就可以求出x了

额....是这个意思啊,看来是我的阅读不行,列了半天式子也没把相关的量组合到一起,题意理解的有误差

谢谢楼上高手的讲解.....