"In a lift accelerated upwards at a certain rate, a spring balance indicates a weight to have a mass of 10kg. When the lift is accelerated downwards at twice the upward rate, the mass appears to be 7kg. Find the actual mass and the upward acceleration of the lift." In short, im stuck. I think this question involves simultaneus equations, but i cant get a set of equations that make sense. Ive looked at the textbooks I have but they all concern themselves with the resistance forces or tensions in the strings.