Shortcut Trick
For a number to be divisible by 36, it must be divisible by its co-prime factors, 4 and 9.
Rule for 4: Last two digits must be divisible by 4 → 47502 is eliminated (02 is not divisible by 4).
Rule for 9: Sum of digits must be a multiple of 9.
Checking remaining options: Sum of digits for 29412 = 2 + 9 + 4 + 1 + 2 = 18 (Divisible by 9).
∴ The correct answer is 29412.
Alternate Method
Given:
Numbers to check: 47502, 29412, 54732, 87064
Concept Used:
Since 36 = 4 × 9 and gcd(4, 9) = 1, any number divisible by 36 must be divisible by both 4 and 9.
Divisibility by 4: The number formed by the last two digits is divisible by 4.
Divisibility by 9: The sum of the digits of the number is divisible by 9.
Calculations:
⇒ Step 1: Check divisibility by 4 (Last two digits)
⇒ 47502 → 02 is not divisible by 4.
⇒ 29412 → 12 is divisible by 4.
⇒ 54732 → 32 is divisible by 4.
⇒ 87064 → 64 is divisible by 4.
⇒ Step 2: Check divisibility by 9 for the remaining numbers (Sum of digits)
⇒ 29412 → 2 + 9 + 4 + 1 + 2 = 18 (18 is divisible by 9)
⇒ 54732 → 5 + 4 + 7 + 3 + 2 = 21 (21 is not divisible by 9)
⇒ 87064 → 8 + 7 + 0 + 6 + 4 = 25 (25 is not divisible by 9)
⇒ Hence, only 29412 satisfies both conditions.
∴ The correct answer is 29412.
Additional Information
Divisibility by Composite Numbers
If a number is divisible by a composite number, it must be completely divisible by all of its co-prime factors (e.g., for 72, check 8 and 9).
Divisibility Rule of 8
A number is divisible by 8 if the number formed by its last three digits is divisible by 8.
Divisibility Rule of 11
A number is divisible by 11 if the difference between the sum of its digits at odd places and the sum of its digits at even places is either 0 or a multiple of 11.