The diagnostic test in the Official Guide is a killer. Don't worry too much about it.
The test is meant to familiarize you with the types of questions found on the GMAT and give you a very approximate idea of your current skills.

Don't dwell too much on the results of this test.

Regarding whether or not 1 month is enough prep time. It's tough to answer that question without a few pieces of key information.
- What's your target score?
- How are your GMAT skills currently?
- How many hours do you intend to study each day?

To get an idea of the required prep time, take an official practice test: https://www.mba.com/the-gmat/download-fr ... tware.aspx
It may be the case that you're already scoring above your target score, in which case you may not need to prepare at all.
Or it may be the case that you're 450 points away from your target score, in which case 1 month will not be enough time.

Finally, about using the Official Guide as your sole resource: The Official Guide is a great resource for official practice questions, but it's not very comprehensive when it comes to instruction. To perform well on the GMAT, you need to learn all of the core concepts AND you need to learn GMAT-specific strategies for answering questions quickly and accurately. In my opinion, the Official Guide does not provide this level of instruction.

Cheers,
Brent

Hi nr120,

You really have to define your goals before we can define whether you have the proper resources and the necessary time to hit your goals. So, let's start with the basics:

1) When are you planning to apply to Business School?
2) What is your goal score for the GMAT?

The Diagnostic quiz in the Official Guide is NOT truly representative of the Official GMAT (beyond the basic content and question types). It's not adaptive, doesn't have the same number of questions (nor the same ratio of question types), isn't on a computer, doesn't include the Essay and IR sections, etc., so your performance on that Test is probably best uses to measure your comfort level with the material. For a true, reasonable assessment of your abilities, you should take a FULL-length practice CAT Test (you can download 2 for free from www.mba.com). A FULL CAT takes about 4 hours to complete, so make sure that you've set aside enough time to take the whole thing in one sitting.

The "short" answer to your question is that 1 month of study time is probably NOT going to be enough for you to hit your score goals. Most Test Takers spend 3 months (or more) on their studies; during that time, 10-15 hours per week (or more) of focused study is common. During a 3-month study period, you'll likely use several study resources, but we can talk through those options later.

For now, you're in the right place. Take the practice CAT, then report back with your scores. As you progress through your studies, you should post your questions in these Forums any time you get stuck. The Experts here can help.

GMAT assassins aren't born, they're made,
Rich