The video below illustrates how to apply the approach of plugging in numbers to solve GMAT problems, and the limitations of this approach. I also compare the plug in approach to the direct approach. Here is the summary of the key points:

**Advantages of Plug in approach:**

- It is easy to implement and the easier algebraic/word problems can often be solved by using simple numbers.
- Sidesteps the necessary algebra. This is one of the main reasons why a lot of test prep books recommend plugging numbers because many students are weak in algebraic procedures.

**Drawbacks of Plug in approach:**

- The choice of numbers to pick is important, because that can influence the amount and complexity of the ensuing numerical work.
- In case of difficult problems, the amount of numerical work and the likelihood of making mistakes increases.
- To be absolutely certain of the correct choice, one needs to test all of the answer choices.
- In case of very difficult problems, the amount of work may exceed the amount of time it may take to approach the problem directly.

**Advantages of direct algebraic approach:**

- Direct and fast, and no need to spend time in thinking about appropriate choice of numbers.
- In case of difficult problems, the most efficient and fastest method is often the direct algebraic approach.
- In case of data sufficiency problems that require one to translate a particular word statement to an algebraic expression and subsequent simplification, the ability to solve the entire question might rest on being comfortable with the direct algebraic approach.
- The harder problems often require a strong grasp of algebraic procedures and this skill is necessary to obtain a high score on the GMAT.

**Drawbacks of direct algebraic approach:**

- Difficult to implement if one is not comfortable with manipulating algebraic expressions and simplifying them with accuracy.