According to the question, 7×11×13=1001, when any 3 digit number is multiplied by 1001 then it repeat itself and always completely divisible by 7,11,13. Let 3 digit number are pqr ⇒pqr×1001=5z3x4y pqr×pqr=5z3x4y Compare both sides ⇒p=5,r=3,q=4 So, p=5=x,q=4=z,r=3=y ∴(x+y−z)=(5+3−4)=4