if k is a positive three-digit integer, what is the hundreds digit of k?

1. the hundreds digit of k + 150 is 4.

2. the tens digit of k + 25 is 7.

why doesn't A work here?

got this from mgmat question bank. thanks for your help.

k could be 280 or 320 and notice the 2 different hundred's digitof k; so statement 1 is INSUFFICIENT.

In general, with problems like this one, just consider the EXTREMES of any possible range they throw at you.

If the hundreds digit of (k + 150) is 4, then take that to mean that
400 <= k + 150 <= 499
or
250 <= k <= 349.

Therefore, the hundreds digit of k can be either 2 or 3, so this statement is insufficient.

Note that you don't have to set up the inequalities to solve the problem: you can just notice that the biggest possible value for (k + 150) is 499, and that the smallest possible value for that expression is 400. In any case, it's much better to consider extremes for a problem like this than to pick numbers like the ones in the previous post (which are, for all intents and purposes, random choices - not the best way to get started on a problem with a definite range of numbers).