A ball and a box weigh 900 grams.
Two identical balls and the same box weigh 1.35kg.
What is the mass of the box?
How do I work this out?
1.35kg = 1350g = 900+450g
2 balls and a box weight 450g more than one ball and the box.
So, a ball weighs 450g
Since a ball and a box weigh 900g, the box also weighs 450g.