Reasoning · Grade 3-2 Weighing Applications
Problem
The top being level makes the whole lower bar 2 g.
Equal arms balance only when the two sides hold the same amount — a see-saw idea every third grader can picture.
3.OA.A.4Draw A DiagramA bar hung from its middle balances only when the two sides carry the same amount.
A level bar is a statement that the two sides are equal, which can then be worked on from both ends at once.
What hangs on one side weighs its pieces added together, so a side's load is fixed by the weights it carries and nothing else.
The lower bar is level too, so the two weights match.
Same idea again: a centered bar balances only when both hanging weights match.
3.MD.A.2Draw A DiagramSplitting 2 g evenly gives 1 g each.
Sharing 2 equally between two ends is simple halving — each end gets 1 g.
3.OA.A.3Work BackwardsA centered bar balances only when both sides weigh the same — so you just share the weight evenly, using Grade 3 halving you already know!