If the number 179x091y is to be divided by 88 , then it must be divided by 8 and 11. We know that if the difference between the sum of digits at even and odd position is divisible by 11 , then the number is also divisible by 11. (7+x+9+y)−(1+9+0+1)=5+x+y To make 5+x+y divisible by 11 , x+y must be equal to 6 . Now, we know that, if last three digits of a number is divisible by 8 , then the number is also divisible by 80. Hence, if y=2, then 912 is exactly divisible by 8. ∴y=2 and x=6−2=4 ⇒x−y=4−2=2