# Bank Identification Number Check Digit Formula Question

• Mar 28th 2010, 01:25 PM
ipatch
Bank Identification Number Check Digit Formula Question
Alright, so I am suppose to use the bank indentification number check digit formula to see if it can detect a check with tranposed digits.

The correct bank ident number is 314970664
The incorrect bank indent # is 319470664

The "4" at the end of the number is the check digit.

Bank Ident. Number Check Digit Formula:

a0 ≡ (7a + 3a + 9a + 7a + 3a + 9a + 7a +3a) mod 10

a0 ≡ (7*3 + 3*1 + 9*9 + 7*4 + 3*7 + 9*0 + 7*6 + 3*6 )

≡ 21 + 3 + 81 + 28 + 21 + 0 + 42 + 18

≡ 1 + 3 + 1 + 8 + 1 + 0 + 2 + 8; The sum = 24 For some reason my book drops the first digit and keeps the second digit or ones digit, I have no clue why it does this.

≡ 24 ≡ 4 (mod 10)

The difference between 24 and 4 is 20, which is a multiple of 10.

Therefore the check digit did not catch the error.

Does there seem to be any problems with my solution?

cheers.
• Mar 28th 2010, 10:41 PM
CaptainBlack
Quote:

Originally Posted by ipatch
Alright, so I am suppose to use the bank indentification number check digit formula to see if it can detect a check with tranposed digits.

The correct bank ident number is 314970664
The incorrect bank indent # is 319470664

The "4" at the end of the number is the check digit.

Bank Ident. Number Check Digit Formula:

a0 ≡ (7a + 3a + 9a + 7a + 3a + 9a + 7a +3a) mod 10

a0 ≡ (7*3 + 3*1 + 9*9 + 7*4 + 3*7 + 9*0 + 7*6 + 3*6 )

≡ 21 + 3 + 81 + 28 + 21 + 0 + 42 + 18

≡ 1 + 3 + 1 + 8 + 1 + 0 + 2 + 8; The sum = 24 For some reason my book drops the first digit and keeps the second digit or ones digit, I have no clue why it does this.

≡ 24 ≡ 4 (mod 10)

The difference between 24 and 4 is 20, which is a multiple of 10.

Therefore the check digit did not catch the error.

Does there seem to be any problems with my solution?

cheers.

No, other than the statement that you made indicating that you do not understand modular arithmetic.

CB