Question

5) a
If 7251239 is a multiple of 11, where z is a digit, what is the value of z?​

Answer 1

If a number is a multiple of 11, difference between sum of the digits at even places and sum of the digits at odd places will be a multiple of 11.

Here, the number is 31z

Sum of the digits at even places = 1

Sum of the digits at odd places =3+z

1 − (3+z) = 11m

−2−z=11m

z can take values 0 to 9

Possible values of −2 − z are 0, 11, 22, 33 etc.

Least value possible for −2 − z is 0

−2−z=0

Therefore,

z=−2

But z cannot be negative.

So, there is no possible positive value of z that will make 31z, a multiple of 11.