To calculate the percentage of 13 marks out of 20, you can follow these steps:

Step-by-Step Breakdown:

1. Identify the formula for percentage:
   The general formula for calculating percentage is:
   $\text{Percentage} = \left( \frac{\text{Obtained Marks}}{\text{Total Marks}} \right) \times 100$

2. Substitute the values:
   In your case, the obtained marks are 13, and the total marks are 20. Plug these values into the formula: $\text{Percentage} = \left( \frac{13}{20} \right) \times 100$

3. Perform the division:
   $\frac{13}{20} = 0.65$

4. Multiply by 100 to get the percentage:
   $0.65 \times 100 = 65$

Final Answer:

13 out of 20 is 65%.

Would you like further details on how percentages work, or have any questions?

Here are some related questions for deeper understanding:

1. How do you convert a percentage back to a fraction?
2. What would 15 out of 25 be as a percentage?
3. How do you increase or decrease a number by a given percentage?
4. How do you calculate percentage error in experiments?
5. How can percentages be used in financial calculations?

Tip: To easily convert a fraction to a percentage, multiply by 100!