How does moving the place of a digit change its value.

It can either reduce or add to its value. Say that you had a number 5. If you move the place it would make it .5 which reduced its value to not even 1. But with the same 5. if you move the place the other way to 50. It increases its value significantly.

Answer is d = 121.51  use the compound interest formulae    a = p (1 + (r/12)/100)^(12*n)  run 2 case  p = 1700  r = 18.7, r = 12.5  n = 1 (as the problem is asking over the course of a year)  solve for a for both the r and subtract the two values of a to obtain ~121.51