 
       
      
    Q3. If  is a multiple of 3, where 
 is a digit, what is the value of 
?
(Since  is a multiple of 3, its sum of digits 
  is a multiple of 3; so 
 is one of these numbers: 0, 3, 6, 9, 12, 15, 18, ... . But since 
 is a digit, it can only be that 
. Therefore, 
. Thus, 
 can have any of four different values.)
 
                
                  if a number is multiple of 3 then the sum of its digits is also a multiple of 3.
Summ of digits of 24x = 2 + 4 + x = 6 + x
6 + x is a multiple of 3 which means
6 + x = 0 or 3 or 9 or 12....
but since x is a single digit the possible sum is 6 or 9 or 12 or 15 and hence value of x are 0 or 3 or 6 or 9 respectively.
hence possible value of x = 0, 3, 6, or 9.
 
                