representing the number 5, and the next character to be read is a 0, then the binary number read so far is
which represents the number 10. Could you start with the knowlege that you had 5, and added a 0 on the end to get a 10? Is the result divisible by 5? If instead the next character to be read was a 1, then the binary number becomes
which represents the number 11. Could you start with the knowlege that you had 5, and added a 1 on the end to get a 11? Is the result divisible by 5 this time?