Divisiblity rule of 11 , Sum of odd place digit - Sum of even place digit equal 0 or 11 . =(4+0+7)−(a+6+b)=11−6−(a+b)=5−(a+b) Possible value of (a+b) is ⇒5−5=0 [∵a+b=5 or a+b=16] ⇒5−(16)=11a+b=16 If difference of sum of odd place digit and sum of even place digit is 0 or 11 then number is divisible by 11. So, only 2 possible value we will get (a+b)=5 and (a+b)=16 So, sum of all positive value of (a+b) is 16+5=21