To solve this problem, you need to calculate 25% of 120.

Calculation:

$\text{Number of students who earned an A} = 25\% \times 120 = \frac{25}{100} \times 120 = 30$

Thus, 30 students earned an A.

The correct answer is 30.

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Would you like a detailed explanation of the steps? Feel free to ask if you need further clarification!

Here are 5 related questions:

1. What is 10% of 200?
2. If 50% of the students in a class are absent, how many students are present?
3. Mrs. West wants to increase her class size by 10%. How many students will she have if she adds 10% to the original 120?
4. If 15% of 200 students earn an A, how many students is that?
5. What is the formula to calculate percentages of a number?

Tip: To calculate a percentage of a number, multiply the number by the percentage (expressed as a fraction or decimal).