Revision Notes for Class 7 Maths Chapter 15: Finding the Unknown

Quick revision notes summarising all key concepts from Class 7 Maths Chapter 15 “Finding the Unknown” — the final chapter of Class 7 Maths. These Class 7 Mathematics Chapter 15 notes are ideal for quick revision just before exams.

• An equation is a statement that two expressions are equal, containing one or more unknowns (like x, y, u) whose value(s) make the statement true.
• Balancing method: whatever operation (add, subtract, multiply, divide) is performed on one side of an equation must be performed identically on the other side, to keep both sides equal — just like keeping a balance scale level.
• To solve an equation, isolate the unknown by moving all other terms to the other side (remembering that a term changes sign, e.g. + becomes -, when moved across the equals sign).
• Always check your solution by substituting it back into the original equation — both sides should come out equal.
• Some equations have no solution — e.g. x + 4 = x + 5 simplifies to 4 = 5, which is never true for any value of x.
• Word problems can be translated into equations by assigning a letter to the unknown quantity, then writing the relationships described in the problem as an equation, solving it, and checking the answer makes sense in context.
• When an equation has brackets, distribute (multiply out) the bracket first before collecting like terms, e.g. 4(m+6) = 4m + 24.
• Two-unknown word problems (like the “heads and feet” puzzle) can be solved by expressing one unknown in terms of the other from one equation, then substituting into the second equation.

See also: NCERT Solutions for Class 7 Maths Chapter 15

Practice more: Extra Questions for Class 7 Maths Chapter 15

For the full chapter, see the Class 7 Maths Formulas Handbook.

Written by Satish

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