Q27.If M is a positive integer, then M^3 has how many digits?

(1) M has 3 digits.

(2) M^2 has 5 digits

   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

碰到这种题目怎么做？

If condition 1 and 2 combined looks promising, I generally look for 2 cases which both satisfy both conditions but have different outcomes (answer to the original question).  The examples are generally boundary conditions.  For example:

Case 1:
smallest M^2 is 10000 where M = 100
M^3 = 1000000, 7 digits

Case 2:
largest M^2 is 99999 where M = 300+
M^3 = 100000*300 ish = 30000000 ish, 8 digits

E

谢谢楼主
不过有点问题:

我和您的做法大致相同,但还是有点差别.我是从M下手,取M的两个极端,一个是100,一个是999,这样的话,就会分别得到它们的平方一个是5位数(100),一个6位数(999),这样我又觉得C选项,把两个条件合在一起用,又可以确定M的值了.

请高手给点指正吧,有点困惑.