In the number 4564M, replace M by the smallest whole number to make the resulting number divisible by 8.
0
A number is divisible by 8, if the number formed by its digits in hundred's place, ten's place and units place are divisible by 8.
In 4564M, the number formed by its digits in hundred's place, ten's place and units place is 64M.
The possible values M can take is either 0 or 8 ,because 643 and 642 is not divisible by 8.
Since 640 and 648 is divisible by 8, the smallest value of M is 0.