刚做完prep1。结局惨烈。几个数学题。求战友们解答。

sdcar2010

If n! = somthing * 11, is n at least as big as 11?

gmat2000

4. an integer greater than 1 that is not prime is called composite. if the two-digit integer n is greater than 20, is n composite?
1) the tens digit of n is a factor of the units digit of n.
2) the tens digit of n is 2.

1) Let's say the units digit of n is a.  Then the tens digit of n is a factor of a.  Therefore, n = 10*m*a + a = a*(10m +1).  Then n has a factor of a and a is bigger than 1 since n is greater than 20.  n is a composite for sure. Sufficient.
2) Insufficient.  21, 22, 23 ....

-- by 会员 sdcar2010 (2011/1/5 11:56:31)

do not understand n = 10*m*a + a, should it be like n = AB = 10xA + AC =A(10+C).. ?

sdcar2010

LS is right. My bad.

mijianture

If you can see the attached picture, you would have a better time to solve the problem 1 LZ posted.

According to the stimulus, [9] = 3*9 =27. [6] = (1/2) * 6 = 3.  So [9]*[6] = 27 * 3 = 81.  So far so good.  But if you choose (a) as the correct answer, you were wrong because (a) is [81] = 3*81 = 243!

On the other hand, (d) [27] = 3*27 = 81, is the right answer!

-- by 会员 sdcar2010 (2011/1/5 22:39:41)

佩服SDCAR的古道热肠，不厌其烦地解释，今天看到题干终于明白了，谢谢你的指点。

sdcar2010

If you can see the attached picture, you would have a better time to solve the problem 1 LZ posted.

According to the stimulus, [9] = 3*9 =27. [6] = (1/2) * 6 = 3.  So [9]*[6] = 27 * 3 = 81.  So far so good.  But if you choose (a) as the correct answer, you were wrong because (a) is [81] = 3*81 = 243!

On the other hand, (d) [27] = 3*27 = 81, is the right answer!

-- by 会员 sdcar2010 (2011/1/5 22:39:41)

佩服SDCAR的古道热肠，不厌其烦地解释，今天看到题干终于明白了，谢谢你的指点。

-- by 会员 mijianture (2011/3/25 14:01:21)

The pleasure is all mine.