求助数学

sharondu

能否告知如何得出的答案，谢谢！

Q3:

If the units digit of the three-digit positive integer k is nonzero, what is the tens digit of k?

(1)     The tens digit of k + 9 is 3.

(2)     The tens digit of k + 4 is 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.

Answer: a

ipatronsaint

这题应该是A吧！

ipatronsaint

一个个位非零的三位数K,他的十位数是几？

k+9后十位数是3。个位非零即在1-9间最小为1，1+9进位，所以十位数应该是2.  sufficient

k+4后十位数是2。十位数可以是2或1.  not sufficient

所以我认为选A

sharondu

Thank you very much,Ipatronsaint. I didn't understand the question. I am so nervous on maths because I am inefficient on it. What should I do if I only have 18 days left for the preparation. My test has been scheduled on 11th July.

lina_cheung

我的解法：

1）题干1可以推出 30≤K+9≤39， 从而得出21≤K≤30，由于题干告知我们Units digit不是零，所以21≤K≤29。推出K的十位数为2。充分。

2）题干2可以退出20≤K+4≤29，从而得出16≤K≤25，推出K的十位数为1或者2，不充分。

ipatronsaint

我准备八月份考了。关于数学我认为有必要将一些英语的数学用语背背强化一下，只是真对看题困难呀，anyway,别灰心加油！！！！