3. The average of 4 numbers is 9. If one of the numbers is 7, what is the sum of the other 3 numbers?
Answer: C
The sum of the other 3 numbers is 29.
To find the sum of the other three numbers, we first calculate the total sum of all four numbers using the average. Since the average is 9, the total sum is 4 times 9, which equals 36. Subtracting the known number, 7, from this total gives us the sum of the other three numbers as 29.
A) 2
This option is incorrect because if the sum of the other three numbers were 2, the total sum would only be 9 (7 + 2), which contradicts the given average of 9 for four numbers.
B) 12
This option is also incorrect. If the sum of the other three numbers were 12, the total would be 19 (7 + 12), which again does not match the calculated total sum of 36 required for an average of 9.
C) 29
This option is correct. With the total sum of the four numbers calculated as 36, subtracting the known number 7 results in 29 for the sum of the other three numbers, matching the requirement for the average of 9.
D) 36
This option is incorrect because if the sum of the other three numbers were 36, the total sum would be 43 (7 + 36), which does not align with the necessary total of 36 for an average of 9 for four numbers.
Conclusion
The correct answer is definitively 29, as it satisfies the requirement derived from the average calculation. All other options fail to provide a sum that aligns with the total needed for the average of the four numbers, demonstrating their invalidity in the context of the question.