Are you struggling with time, distance, and speed problems on the GRE? Remember the basic formula Distance=Rate x Time. This can be adjusted to Rate=Distance/Time or Time=Distance/Rate. Also, you may want to review the lesson video Ratios and Rates if you haven't seen it in a while.
Easy problems may have a straightforward application of this formula, but the GRE also has more complicated questions using this principle. This blog post offers an example of a basic distance question. Notice how you can solve the problem both by plugging in the answer choices and by solving the algebraic equation.
One way rate problems can become more complicated is when multiple objects are moving. For example, here are two blog posts using trains. The fist blog post asks you to solve for two trains traveling in the same distance. This example demonstrates how for any entities headed in the same direction, the difference between the two rates is the amount the faster entity is outpacing the slower one per hour. The second blog post is an example of two trains head towards one another. In this case, you must add their rates to find their total rate.
The best way to prepare for these types of problems is to know the basic formula and practice applying it in various scenarios. With that being said, you are likely to only see a couple of these questions on the test day, so don't stress too much if you are struggling with these types of questions :)
If you have the official guide, here are some explanations for rate problems you might find useful: