Question

If31z5is a multiple of 3, where zis a digit, what might be the values of z?

Answer 1

Since 31z5 is a multiple of 3, the sum of its digits will be amultiple of 3.

That is, 3 + 1 + z+ 5 = 9 + z is a multiple of 3.

This is possible when 9+ z is any one of 0, 3, 6, 9, 12, 15, 18, and so on …

Since z is asingle digit number, the value of 9 + z can only be 9 or 12 or15 or 18 and thus, the value of x comes to 0 or 3 or 6 or 9respectively.

Thus, z can haveits value as any one of the four different values 0, 3, 6, or 9.