Final answer:
To calculate the success rate, divide 21 by 39 to get approximately 0.5385, which rounds to 0.538 or 53.8% success rate.
Step-by-step explanation:
To find the part of the time the basketball player was successful in making free throws, we divide the number of successful throws by the total number of attempts and then convert the result to a decimal. The player made 21 out of 39 free throws.
- Calculate the success rate: 21 / 39
- Divide to get a decimal: Approximately 0.5385
- Round to the nearest thousandth: 0.538 (since the digit after the third decimal place is less than 5, there's no need to round up)
The player was successful 53.8% of the time, to the nearest thousandth.