Work Backwards to Recover a Start Value
Given the end state of a chain of operations (or a calculation done wrongly), invert each step in reverse order to recover the original number or position. It begins with undoing simple add/subtract or skip-counts, then reversing a wrong product, undoing geometric moves, and unwinding multi-step decimal and fraction operations. Inversion is the universal 'the result was...' strategy.
grade 2–4 GMDNBTNFOA Work BackwardsConvert to Algebra
Progression (9)
2-2 1. Skip-count backward to the start 4.NBT.A.2
2-2 2. Recover the unknown, then recompute 3.OA.A.43.OA.B.6
2-2 3. Undo more/less to find original length 2.MD.B.5
3-1 4. Reverse the operations to find the start 3.OA.D.83.OA.A.4
3-2 5. Recover the original number from a wrong product 3.OA.A.43.OA.C.7
4-1 6. Reverse the moves to recover original 4.G.A.3
4-2 7. Undo a wrong fraction operation to recover the start 4.NF.B.3
4-2 8. Reverse decimal operations to recover the start 5.NBT.B.7
4-2 9. Undo a wrong decimal operation to recover the start 5.NBT.B.7