Given: Six digits number is 25a64b Concept used: Divisibility rule of 11, says, in a number when we add even place digits and subtract it from the sum of odd place digits, results will be either 0 or multiple of 11 Calculation: In digits 25a64b, the sum of odd place digits =2+a+4 ⇒6+a the sum of even place digits =5+6+b ⇒11+b According to the divisibility rule of 11, The sum of odd place digits – the sum of even place digits = 0 ⇒6+a–(11+b)=0 ⇒a–b=11–6 ⇒a–b=5 ∴ The value of (a – b) is 5.