Mod 10 ?? Need correction please !

Question

0

624

1

+191

Hello, guys ! I need correction please :/

Is the following ISBN number valid : 978-1-246548-50-7 ?

I found No : I found 109 mod 10 so 10-9 = 1 and I should have found 7 if its was the right ISBN right ?

I did D13 = 10 - ( 9 + 3*7 + 8 + 3*1 + 2 + 3*4 + 6 + 3*5 + 4 + 3*8 + 5 + 3*0 )

Thank you for your help !

Best,

Thalys

Thalys Oct 1, 2015

Rom · Answer 1 · 2015-10-01T08:46:15

109 is the correct number for the sum.

\(109 \bmod{10} = 9\\ 10-9 = 1\\ D[13] = 7 \neq 1\\ \mbox{So this is not a valid ISBN}\)