mugzy is right about approach fuel.
re your 250kg S/T + T/S, often the question will give you a starting weight which is a Brakes Release Weight (BRW), which will have already burnt your 150kg start up fuel, so you only need to add 100kg for taxi and shutdown. If the question gives you a weight at the ramp or fuel at engine start up or something like that then you have to factor in the whole 250kg