Shortcut Trick
For a number to be divisible by 72, it must be divisible by both 8 and 9.
Divisibility by 8: Last three digits 6x2 must be divisible by 8. If x = 3, 632 ÷ 8 = 79 (True).
Divisibility by 9: Sum of digits (9+1+8+7+6+x+2) = 33 + x must be divisible by 9.
If x = 3, 33 + 3 = 36, which is divisible by 9.
∴ The correct answer is 3.
Alternate Method
Given: Seven digit number 91876x2 is divisible by 72.
Formula Used: Divisibility rule of 72 = Divisibility by 8 × Divisibility by 9.
⇒ Divisibility by 8: Check 6x2. Possible values for x are 3 (632) or 7 (672).
⇒ Divisibility by 9: Sum = 9 + 1 + 8 + 7 + 6 + x + 2 = 33 + x.
⇒ For 33 + x to be a multiple of 9, the nearest multiple is 36.
⇒ 33 + x = 36 ⇒ x = 3.
⇒ Checking x = 7: 33 + 7 = 40 (Not divisible by 9).
∴ The correct answer is 3.
Additional Information
Divisibility by 8
A number is divisible by 8 if the last three digits are divisible by 8 or are all zeros.
Divisibility by 9
A number is divisible by 9 if the sum of its digits is divisible by 9.
Composite Divisibility
To check divisibility by a composite number n, the number must be divisible by its co-prime factors (e.g., 72 = 8 × 9).