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Rewrite the Condition into the Block You Need

Some questions ask for an expression rather than the letters -- a ratio x/y, a sum over a product, a reciprocal sum -- and some systems hide the letters inside a repeated block such as 1/x. Instead of solving for each letter, reshape the given condition until it produces exactly that block and substitute it whole, or rename the repeated block as a new unknown and solve the simpler system it makes. Sometimes the value comes out though the letters are never pinned down; when the blocks themselves are solved, the original letters can be recovered from them.

grade 7–8 Expressions Convert to AlgebraIdentify Subproblems

Builds on: Say It in LettersProportion and Proportional Division

Progression (8)

g7 1. Equal side products cancel the shared corner Number systemExpressions · foundational
g7 2. A relation fixes a ratio, so the expression is constant Expressions · foundational
g7 3. Rewrite numerators using the given total Expressions · core
g7 4. Turn the condition into x+y in terms of xy ExpressionsNumber system · core
g7 5. Clear denominators to reshape the condition Expressions · advanced
g7 6. Sum of reciprocals is sum over product Expressions · advanced
g8 7. Rename repeated reciprocals to get a linear system Expressions · advanced
g8 8. Times give equations in reciprocal speeds ExpressionsRatios · advanced