~几道数学提求助

莫里亚提

1.
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 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.

答案是 C， 我的问题是怎么从（1）得出呢？0.15x+0.29y=4.4, 然后一个一个的配吗？

2.

图弄不过来……是 GWD数学2 的 第30题In the figure, each side of square ABCD has length 1, the length of line segment CE is 1, and the length of line segment BE is equal to the length of line segment DE.What is the area of the triangular region BCE?



A.1/3

B.(Ö2)/4

C.1/2

D.(Ö2)/2

E.3/4


答案是 B, 不知道怎么算……

3.
How many seconds will it take for a car that is traveling at a constant rate of 45 miles per hour to travel a distance of 22 yards?(1 mile = 1,160 yards)



A.8

B.9

C.10

D.11

E.12


答案是 C, 为什么我算不出来啊……智商啊……

4.
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 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.

答案是 C, 我用了几个数试试选出来的，有什么别的方法吗？

急需牛人解答~十分感谢！！

图弄不过来……是 GWD数学2 的 第30题In the figure, each side of square ABCD has length 1, the length of line segment CE is 1, and the length of line segment BE is equal to the length of line segment DE.What is the area of the triangular region BCE?



A.1/3

B.(Ö2)/4

C.1/2

D.(Ö2)/2

E.3/4


答案是 B, 不知道怎么算……

3.
How many seconds will it take for a car that is traveling at a constant rate of 45 miles per hour to travel a distance of 22 yards?(1 mile = 1,160 yards)



A.8

B.9

C.10

D.11

E.12


答案是 C, 为什么我算不出来啊……智商啊……

4.
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 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.

答案是 C, 我用了几个数试试选出来的，有什么别的方法吗？

急需牛人解答~十分感谢！！

sinuolee

第一题我认为是先看（1），明显不能解出来，再看（2），列出你的那个式子，需要的条件就是总共等于4.4这样就可以求出答案，所以选C
第二个图题，EC延长至BC的交点F，三角形BEF和EDF全等,先求出BEF的面积（因为是直角），减去三角形BFC的面积，就等于所求的了。。。
第三题，我也没有做出来，我等于一个分数，确定题没有问题么？

莫里亚提

谢谢你的解答。
第一题我写错了，答案是D.我不知道从（1）得出答案是只能靠配吗？
第二题我比较囧，当时看到题目就把它当做立体的了……看了你的解答恍然大悟……
第三题我也觉得答案错了。
请问第四题你会做吗？
再次感谢^^

红红的云

4.  here's the theory:
- if n is not divisible by 2, then n is odd, so both (n - 1) and (n + 1) are even. moreover, since every other even number is a multiple of 4, one of those two factors is a multiple of 4. so the product (n - 1)(n + 1) contains one multiple of 2 and one multiple of 4, so it contains at least 2 x 2 x 2 = three 2's in its prime factorization.
- if n is not divisible by 3, then exactly one of (n - 1) and (n + 1) is divisible by 3, because every third integer is divisible by 3. therefore, the product (n - 1)(n + 1) contains a 3 in its prime factorization.
- thus, the overall prime factorization of (n - 1)(n + 1) contains three 2's and a 3.
- therefore, it is a multiple of 24.
- sufficient

莫里亚提

Thank you so much~

hsuyinfeng

其实   第一题  第一个statement 仔细思考一下  不难  因为邮票是整数  所以这个 整数解 只有10  仔细试一两个数 你就明白  本题中 设定0.15 and 0.29是有特别意义的

hsuyinfeng

第三题  题目 肯定错了 最起码 1 mile = 1760 yards  另外 题干上 不是22 应该是220  这样的话 就是10秒

wxch

第一题选A吧？条件二得不出具体的数啊