Which of the following number is divisible by both 9 and 11?

Correct option is A

Given:
The given options are 7920, 8250, 8020, and 8163.
Formula Used:
Divisibility by 9: The sum of digits must be a multiple of 9.
Divisibility by 11: The alternating sum of digits must be 0 or a multiple of 11.
Solution:
Test option A: 7920.
Sum of digits = 7 + 9 + 2 + 0 = 18. Since 18 is divisible by 9, the number is divisible by 9.
Alternating sum of digits = 7 - 9 + 2 - 0 = 0. Since the difference is 0, it is divisible by 11.
Thus, 7920 is divisible by both 9 and 11.
Final Answer
So the correct answer is (a)