Question

write a digit in the blank space of each of the following numbers so that the numbers formed is divisible by 11:8_9484

Answer 1

Let a be placed in the blank.
Sum of the digits at odd places = 4 + 4 + a = 8+a
Sum of the digit at even places = 8 + 9 + 8 = 25
Difference = 25 - (8-a) = 17 - a
For a no. to be divisible by 11, this difference should be zero or a multiple of 11.
If 17 - a = 0
then, a = 17
This is not possible.
A multiple of 11 has to be taken..taking 11 we obtain 
17 - a = 11
a = 6
Therefore the required digit is 6..

Answer 2

sum of odd place =8+9+8 
                          = 25
sum of even place=?+4+4
                             =?+8
product of even and odd place=25-8
                                                 =17                              
as 11 divisibility rule is that :
1 add all odd places.
2 add all even places
3 find the product of odd an even places
4 if the product is 11,0 
5 then it is divisible by 11    

so product is 17 and 17 is not 11 factor so in the blank we should add 6

869484 is the answer