The number that is 50% greater than 60 is 90.

To find the number that is 20% less than 150, we first calculate the amount that is 20% of 150.

20% of 150 = (20/100) * 150 = 30

Therefore, the number that is 20% less than 150 is 150 - 30 = 120.

Now, we need to determine the percentage by which 90 is less than 120.

To calculate the percentage decrease, we use the formula:

Percentage decrease = (Original Value - New Value) / Original Value * 100

In this case, the original value is 120 and the new value is 90.

Percentage decrease = (120 - 90) / 120 * 100 = 30 / 120 * 100 = 25%

Therefore, the number that is 50% greater than 60 is 25% less than the number that is 20% less than 150.

Math Rules for GMAT:

1. Understand the question: Read the question carefully and make sure you understand what is being asked. Identify the key information and variables involved.

2. Break down complex problems: Break down the problem into smaller, manageable parts. This can help you avoid confusion and make it easier to solve.

3. Use relevant formulas and equations: Familiarize yourself with the formulas and equations commonly used in GMAT math problems. Practice applying them to different types of problems.

4. Simplify expressions: Look for opportunities to simplify expressions by factoring, canceling out common terms, or using known mathematical properties. This can help streamline calculations and make the problem more manageable.

5. Plug in numbers: If you're unsure how to approach a problem, try plugging in numbers to see if you can identify a pattern or rule. This can help you gain insight into the problem and guide you towards the correct solution.

6. Check your work: Always double-check your calculations and ensure that your answer makes sense in the context of the problem. Look for any errors or inconsistencies that may have occurred during the solving process.

Overall, it's important to practice solving a variety of math problems to become familiar with the different concepts and strategies that may be tested on the GMAT.