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sdcar2010

LS NN，为什么不考虑数字3。。？？

-- by 会员 AlohaDJ (2010/12/29 2:03:38)

Oops!

sdcar2010

I think this math question is the same as the one I solved on another thread:

今天考试碰到一道诡异输血让人很惊奇。现在有1 2 3 4 5 五个数，随意组合成三个相加，得出的数x能有1 2 3 4 5 表示。
比如：  12+34 +5=51
DS题， 下面什么情况下能保证所加之和x为偶数。
（1）X是3位数
(2)有一个 加号在1 2中间， 如 31+42。。。

For this question, it is important to realize that the one's digit of the three numbers has to be chosen from two setups of (2, 4, 5) and (3, 4, 5) because the one's digit of x has to be chosen from 1-5, more like only 1 or 2. Any if only one setup works under the condition, that condition is sufficient.

1) insufficient. 123 +4 +5=132,  132 +4 +5= 141
2) inufficient. 32 +14 + 5 = 51, 23 + 14 + 5 = 42

1) and 2) together: Since 1 and 2 has to be separated and X is a 3-digit number, then we have to go with the (2,4,5) setup.  The reason is that for the (3, 4, 5) setup, 1 and 2 have to be together in order to have x greater than 100. But this is not alowed in condition (2).  So we have to go with (2, 4, 5).

One possible example is 2 + 314 + 5 = 321

So 1) and 2) together will give an odd number.

Choose E since none conditions can give you an EVEN number, although 1) and 2) can give you an even number.

AlohaDJ

OH...You have given the solution to the above question!

windychen0089

I think this math question is the same as the one I solved on another thread:

今天考试碰到一道诡异输血让人很惊奇。现在有1 2 3 4 5 五个数，随意组合成三个相加，得出的数x能有1 2 3 4 5 表示。
比如：  12+34 +5=51
DS题， 下面什么情况下能保证所加之和x为偶数。
（1）X是3位数
(2)有一个 加号在1 2中间， 如 31+42。。。

For this question, it is important to realize that the one's digit of the three numbers has to be chosen from two setups of (2, 4, 5) and (3, 4, 5) because the one's digit of x has to be chosen from 1-5, more like only 1 or 2. Any if only one setup works under the condition, that condition is sufficient.

1) insufficient. 123 +4 +5=132,  132 +4 +5= 141
2) inufficient. 32 +14 + 5 = 51, 23 + 14 + 5 = 42

1) and 2) together: Since 1 and 2 has to be separated and X is a 3-digit number, then we have to go with the (2,4,5) setup.  The reason is that for the (3, 4, 5) setup, 1 and 2 have to be together in order to have x greater than 100. But this is not alowed in condition (2).  So we have to go with (2, 4, 5).

One possible example is 2 + 314 + 5 = 321

So 1) and 2) together will give an odd number.

Choose E since none conditions can give you an EVEN number, although 1) and 2) can give you an even number.

-- by 会员 sdcar2010 (2010/12/29 3:30:08)

I think this math question is the same as the one I solved on another thread:

今天考试碰到一道诡异输血让人很惊奇。现在有1 2 3 4 5 五个数，随意组合成三个相加，得出的数x能有1 2 3 4 5 表示。
比如：  12+34 +5=51
DS题， 下面什么情况下能保证所加之和x为偶数。
（1）X是3位数
(2)有一个 加号在1 2中间， 如 31+42。。。

For this question, it is important to realize that the one's digit of the three numbers has to be chosen from two setups of (2, 4, 5) and (3, 4, 5) because the one's digit of x has to be chosen from 1-5, more like only 1 or 2. Any if only one setup works under the condition, that condition is sufficient.

1) insufficient. 123 +4 +5=132,  132 +4 +5= 141
2) inufficient. 32 +14 + 5 = 51, 23 + 14 + 5 = 42

1) and 2) together: Since 1 and 2 has to be separated and X is a 3-digit number, then we have to go with the (2,4,5) setup.  The reason is that for the (3, 4, 5) setup, 1 and 2 have to be together in order to have x greater than 100. But this is not alowed in condition (2).  So we have to go with (2, 4, 5).

One possible example is 2 + 314 + 5 = 321

So 1) and 2) together will give an odd number.

Choose E since none conditions can give you an EVEN number, although 1) and 2) can give you an even number.

-- by 会员 sdcar2010 (2010/12/29 3:30:08)

If it is like what you said " So 1) and 2) together will give an odd number" , then you need to choose the answer C instead of  E,  because you know the answer is "NO".

For me, choosing E is because when, for example, 1+2+534=537 it is a odd number and when, for another example, 1+345+2=348, but it's an even number. The two samples above both meet the criterias:（1）X是3位数
(2)有一个 加号在1 2中间， 。。。so we cannot answer the quesiton if N is an even number or a odd number, choose answer E. I don't know if my reasoning is right!