Suppose the fourth digit of the ISBN 0-71x7-1011-0 is obscured. What is the missing digit?
A) 2
B) 3
C) 6
D) The missing digit can't be determined.

Question

Quizplus · Accepted Answer

The ISBN-10 check digit is calculated using a weighted sum of the first 9 digits, where each digit is multiplied by its position (1 to 9), and the sum is taken modulo 11. For the ISBN 0-71x7-1011-0, the equation is: (0*1 + 7*2 + 1*3 + x*4 + 7*5 + 1*6 + 0*7 + 1*8 + 1*9) % 11 = 0. Solving for x gives x = 6.

Suppose the Fourth Digit of the ISBN 0-71x7-1011-0 Is Obscured