Final answer:
The correct answer is option C.The correct answer to how many counters can be added to 24 without regrouping is 12 (option C). Regrouping is not needed as the sum stays within the ones place without overflowing into the tens place.
Step-by-step explanation:
The correct answer is option C, which is adding 12 counters without regrouping. In arithmetic, particularly when dealing with addition, regrouping is a process used when a sum in any given place value column exceeds a single digit (i.e., 10 or more in the base-10 number system).
To add without regrouping implies that the sum of the numbers in any column does not require carrying over to the next higher place value. Starting with 24 counters, you can add 12 more counters to reach 36. Adding 12 counters to the 24 results in the ones place changing from 4 to 6, which does not necessitate regrouping. However, if you were to add a number that changes the tens place (such as option D, which is 15), regrouping would be necessary because the sum would be 39, where the 3 in the tens place is a result of regrouping from the ones place.