Shortcut Trick
For divisibility by 88, the number must be divisible by both 8 and 11.
For divisibility by 8, the last three digits 8y2 must be divisible by 8 → y = 3 (as 832 ÷ 8 = 104).
For divisibility by 11, the difference between sum of odd position digits and even position digits must be 0 or a multiple of 11.
Sum of odd positions (1st, 3rd, 5th, 7th, 9th) = 1 + 3 + x + 5 + y = 9 + x + y = 12 + x (since y = 3).
Sum of even positions (2nd, 4th, 6th, 8th, 10th) = 3 + 0 + 5 + 8 + 2 = 18.
To make (18) − (12 + x) = 0 → 6 − x = 0 → x = 6.
Thus, x + y = 6 + 3 = 9.
∴ The correct answer is 9.
Alternate Method
Given: The 10-digit number is 1330x558y2 and it is divisible by 88.
Formula Used:
A number is divisible by 88 if it is divisible by both 8 and 11 (co-prime factors of 88).
Divisibility rule of 8: Last 3 digits must be divisible by 8.
Divisibility rule of 11: Absolute difference of the sum of digits at odd places and even places must be 0 or divisible by 11.
Calculations:
⇒ Divisibility by 8 check: last three digits = 8y2
⇒ For y = 3, 832 ÷ 8 = 104 (completely divisible)
⇒ Therefore, y = 3
⇒ The 10-digit number becomes 1330x55832
⇒ Divisibility by 11 check:
⇒ Sum of digits at odd places = 1 + 3 + x + 5 + 3 = 12 + x
⇒ Sum of digits at even places = 3 + 0 + 5 + 8 + 2 = 18
⇒ Difference = 18 − (12 + x) = 6 − x
⇒ For the difference to be 0, 6 − x = 0
⇒ x = 6
⇒ Value of (x + y) = 6 + 3 = 9
∴ The correct answer is 9.
Additional Information
Divisibility Rule of 8
A number is divisible by 8 if the number formed by its last three digits is divisible by 8, or if the last three digits are all zeros.
Divisibility Rule of 11
A number is divisible by 11 if the absolute difference between the sum of the digits at odd positions and the sum of the digits at even positions is 0 or a multiple of 11.
Composite Divisibility
To check divisibility by a composite number like 88, express it as a product of co-prime numbers (e.g., 8 × 11). The number must be divisible by each of these co-prime factors.