binary & decimal representations of int. - N, M are int, formed by reverse ...

**cassiopeia1289** · November 5th 2008, 05:51 PM

Bank ID number is 237(a4)18538 and has an illegible 4th digit.
Determine the value of a4.

They also give the check digit formula, so a9 = 7(a1) + 3(a2) + 9(a3) + 7(a4) + 3(a5) + 9(a6) + 7(a7) + 3(a8) (mod 10)

**Soroban** · November 5th 2008, 06:50 PM

Hello, cassiopeia1289!

Bank ID number is: . $237(a_4)18538$ and has an illegible 4th digit.
Determine the value of $a_4.$

They also give the check-digit formula:
. . $a_9 \:= \:7(a_1) + 3(a_2) + 9(a_3) + 7(a_4) + 3(a_5) + 9(a_6) + 7(a_7) + 3(a_8) \pmod{10}$

Using the check-digit formula:

. . $8 \:=\:7(2) + 3(3) + 9(7) + 7(a_4) + 3(1) + 9(8) + 7(5) + 3(3) \pmod{10}$

. . $8 \:=\:7(a_4) + 205 \pmod{10}$

We have: . $7(a_4) \:=\:\text{-}197 \pmod{10}$

. . . . . . . . $7(a_4) \:=\:3 \pmod{10}$

. . . . . . . . . $a_4 \:=\:9$

**cassiopeia1289** · November 5th 2008, 07:05 PM

awesome, thank you!

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