Question

Correct answers only please!

What is the check digit, d, for the VISA number shown below?

4328 3103 2635 108d


A. 1

B. 3

C. 5

D. 7

Answer 1

D.) 7

Explanation:

To calculate the check digit, multiply every even-position digit (when counted from the right) in the number by two. If the result is a two digit number, then add these digits together to make a single digit (this is called the digital root):

Odd numbers: (1.)= 8 (3.)= 4 (5.)= 6 (7.)= 0 (9.)= 4 (11.)= 6 (13.)= 2 (15.)=(1 + 6)= 7

Even numbers: (2.)= 3 (4.)= 8 (6.)= 1 (8.)= 3 (10.)= 6 (12.)=5 (14.)=0

To this total, we then add every odd-position digit:

Odd = 37

Even = 26

This will result in a total:

37 + 26 = 63

The check-digit is what number needs to be added to this total to make the next multiple of 10:

Next multiple of 10 is 70.

70 - 63 = 7

Answer:

7

Hope this helps : D

Answer 2

D. 7

Explanation:

Divide the number into odd-numbered and even-numbered digits (starting counting digit number 1 from the right).

odd digits: d, 0, 5, 6, 3, 1, 8, 3 . . . . sum of 26+d

even digits: 8, 1, 3, 2, 0, 3, 2, 4 . . . sum of 23

Multiply the sum of even-numbered digits by 2, and add 1 for each even-numbered digit* that is 5 or greater: 23×2 +1 = 47

Add this to the sum of odd-numbered digits, and choose "d" so the result is a multiple of 10.

47 + (26+d) = 73+d

The next higher multiple of 10 is 80. For the total to be 80, d = 7.

_____

* The actual algorithm is described as "for each product of a digit and 2 that is greater than 9, subtract 9 from the product." Doing that, the number added to the sum will be ...

• for 5: 2×5 - 9 = 1
• for 6: 2×6 - 9 = 3
• for 7: 2×7 - 9 = 5
• for 8: 2×8 - 9 = 7
• for 9: 2×9 - 9 = 9

In each case, the number contributed to the sum is 1 more than twice the digit, mod 10.