问一题菜菜数学的思路.....

connie4895

Q9:

How many years did Dr. Jones live?

(1)   If Dr.

Jones had become a doctor 10 years earlier than he did, he would have been a doctor for exactly 2/3 of his life.

(2) If Dr.

Jones had become a doctor 10 years later than he did, he would have been a doctor for exactly 1/3 of his life.

                  

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.

 

是涛涛第26套里面的....请教一下此题的思路。

 

答案是(C)

                                                                                                              

florafox

。。。。。。。。。。。。。。。。。。。。。

claire123jum

x-the age Dr. Jones became Dr.

y-the age he is right now

(x-10)=1/3(y)

(x+10)=2/3(y)

y=60, x=30

c

connie4895

谢谢楼上的详解，其实我的公式设出来也是这样的，但是二式相加之后不是只能得到2X=Y吗?? 这样没有办法得到具体的数字啊!! 所以我才选(E), 实在不懂.....可以麻烦您再详细解释一下吗?? 谢谢!

connie4895

Could anyone hlep? thanks!

minami242

你把二式相减不就完了么。

connie4895

感谢楼上.....脑筋打死结了....没想过用减的....呵!

绝版牙牙

以下是引用connie4895在2008-8-8 16:46:00的发言：
谢谢楼上的详解，其实我的公式设出来也是这样的，但是二式相加之后不是只能得到2X=Y吗?? 这样没有办法得到具体的数字啊!! 所以我才选(E), 实在不懂.....可以麻烦您再详细解释一下吗?? 谢谢!

二式相加也没有问题啊，你得到2x=y，随便代入哪个式子都可以求出x和y啊。这种解法叫做代入法。

两个式子直接相减解除y，然后求出x也可以，这种解法叫消元法。

代入法和消元法是二元一次方程的两种标准解法。