which strategy to adopt?

Nice! Well, when some topics are harder for you, it's not necessarily harder for everyone. The way the GMAT categorizes HARD is when they make past users take the "experimental" questions and they categorize HARD as those questions a lot of test takers didn't get correct.

So the fuzzy area is in the middle which is probably what you're experiencing. Some questions are easier for others but harder for you. Just make sure you get the first set of 3 or 4 questions correct on the GMAT, otherwise since the test is adaptive it'll start putting you in the lower bucket of scores if you get the easy ones in the beginning wrong. So make sure you get easy ones (that the GMAT says are easy) right!

You are absolutely right.
Thanks a lot for your answer!

Hi ceo,

GMATpill is correct that 'difficulty' is a nebulous concept. However, there is also another possible explanation for your trouble with basic problems. Are you using strategies to take them apart, or focusing on the straightforward math?

For many students, 'easy' problems are in some ways the most dangerous simply because it's easy to get complacent. You can look at the problem and go "I can do this" and dive right in--whereas a difficult question forces you to analyze the question, figure out what you're looking for, and consider useful math strategies like Picking Numbers and Backsolving. If the lower-difficulty problems are tough for you, than try using these strategies even on the problems you 'know' you can do, to improve your efficiency and accuracy.

Hope this helps!