dear paras, your question has many possibilities, and it could be solved even without the number next door (which is always unknown to us). The answe can be found by the lowest common multiple theory or it could be simply done by breaking 36 down into integerial factors which are 1X2X2X3X3, it has several outcomes. 2,2 and 9 2,3 and 6 3,3 and 4 1,4 and 9 1,6 and 6 can be eliminated since she has the oldest child which could not be one between the twins. cheers