Manhattan 5th strategy and official guide 13th edition

Those versions are perfectly good to prepare for the GMAT.

Since you have those resources, you might consider signing up for Beat The GMAT's free 60-Day Study Guide (https://www.beatthegmat.com/mba/gmat-guide). Over 40,000 Beat The GMAT students have already done so.
Each day, you'll receive an email with a series of learning activities that guide you, step-by-step, from Day 1 to test day. This will ensure that you will cover everything that the GMAT tests.

Here's an outline of all 60 emails: https://www.beatthegmat.com/mba/gmat-guide-outline

Cheers,
Brent

Hi november22,

The GMAT has not changed in the last year, so these books (which were suitable to study with last year), are still suitable to study with now. Your score on Test Day is based on the work that you do and the points that YOU earn. You will likely need more than an assortment of books to score at a high level, but that's a different issue.

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

Totally agree with Rich on this one. I happen to be a fan of our books (biased of course.) But, the books are only words on pages -- it is the plan you will put together to figure out how to best use those books that will really matter.

I'm including tow great articles here from my old friend Stacey -- really insightful on how to put together a study plan, etc.

https://www.manhattangmat.com/blog/index ... an-part-1/
https://www.manhattangmat.com/blog/index ... an-part-2/

Hope this helps!

-Brian

november22 wrote:After I study whole chapter of Manhattan Strategy Guides, I notice that problem sets at end of chapters are very challenging.

I'm sure there's an argument to be made for "I wish they all felt very easy" -- but, there's value in understanding that the content you are learning is testing and stretching you. It may require you to spend more time preparing for this exam than you had originally anticipated -- but better to learn that early in the process!