if I have an amount which is Composed from two things like object A and Object B, so lets assume the weight of that amount is 50, and given the weight of object A as 10, if I want to calculate the weight of object B then I do 50-10=40 and that's the weight of object B, my question is .. how do I imagine that subtraction? I mean I find it hard to analog that subtraction in my head on something more senseable in real life, is there any good analogy to imagine for subtraction amounts/adding quantities to each other?! how should I exactly imagine a quantity (

*NUMBER*) in my head as what? if I succeed to imagine correctly what's the "quantity" then all the manipulation on it would be more easier .. so please help me as much as you guys can!

thanks