Which of the numbers given below is divisible by 11?
- AOption (a)
359247615447536920
- BOption (b)
359247615447536923
- COption (c)
35924761544753698
- DOption (d)
359247615447536915
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Correct answer
359247615447536915
Why this answer is correct
Shortcut Trick
Apply the divisibility rule of 11: The difference between the sum of digits at odd places and the sum of digits at even places must be 0 or a multiple of 11.
For option (4): 359247615447536915
Sum at odd places: 3+9+4+6+5+4+5+6+1 = 43
Sum at even places: 5+2+7+1+4+7+3+9+5 = 43
Difference = 43 − 43 = 0, which is divisible by 11.
∴ The correct answer is 359247615447536915.
Alternate Method
Given number: 359247615447536915
Formula Used: Divisibility by 11 ⇒ (Sum of digits at odd positions) − (Sum of digits at even positions) = 11k (where k is an integer).
Calculations:
⇒ Let S1 = sum of digits at 1st, 3rd, 5th... places
⇒ S1 = 3 + 9 + 4 + 6 + 5 + 4 + 5 + 6 + 1 = 43
⇒ Let S2 = sum of digits at 2nd, 4th, 6th... places
⇒ S2 = 5 + 2 + 7 + 1 + 4 + 7 + 3 + 9 + 5 = 43
⇒ Difference = |S1 − S2|
⇒ Difference = |43 − 43| = 0
⇒ Since the difference is 0, the number is divisible by 11.
∴ The correct answer is 359247615447536915.
Additional Information
Divisibility by 3 and 9
A number is divisible by 3 or 9 if the sum of its digits is divisible by 3 or 9 respectively.
Divisibility by 4 and 8
A number is divisible by 4 if its last two digits are divisible by 4, and by 8 if its last three digits are divisible by 8.
Alternating Sum Property
For divisibility by 11, you can also subtract and add digits alternately from left to right (e.g., 3−5+9−2...). If the result is 0 or divisible by 11, the number is divisible by 11.
