All of the following SAT Math tests are completely free. There are currently 8 official practice tests. You can download them here or take them online at Khan Academy.
You can find the scoring guides and answer explanations on the official College Board website.
Best overseas education consultants say that the official SAT prep book is not worth purchasing because it's all available for free online. The only reason you might want to buy it is that it includes eight of the practice tests listed above in print form so you don't have to print them out yourself (it's missing tests 2 and 4).
Where Are Practice Tests 2 and 4?
You probably noticed that Practice Test 2 and Practice Test 4 are missing from the section above. That's because the College Board has removed them from their list of officially available practice tests.
Official Math SAT Prep at Khan Academy
If you want a little extra prep (which you likely will since there aren't many official practice tests), there are a bunch of official Math practice questions available as part of Khan Academy's free SAT prep. To access them, you'll need to sign up for an account, but it's free and tracks your progress over time.
At Khan Academy, the SAT lessons and practice questions are divided by type, so they're very helpful for more targeted studying. There's a lot of math content, which can help you brush up on concepts you might have missed or forgotten. You can see a sample Math question below:
Math Practice Questions on the Official SAT Website
Finally, the College Board offers a short SAT Math practice section on its website. This feature includes 30 calculator questions and 18 no-calculator questions. These are all different from those in the 10 practice tests above, so if you'd like more SAT Math practice, this is a great resource to use.
The only drawback to these online SAT Math questions is that they're not given in a practice test format—rather, you'll be shown the correct answer after every question. Nevertheless, the quality of these questions is unbeatable.