Variable
- CBSE · NCERT Class 7 Part 1, Ch 4 Expressions using Letter-Numbers
- CBSE · NCERT Class 9, Ch 2 Introduction to Linear Polynomials
A variable is a letter, such as x or n, that stands for a number which can change or is not yet known.
A variable lets you write one rule that works for many numbers. If one pen costs 12 rupees, n pens cost 12 × n rupees. Here n is the variable. It can be 1, 5 or 100.
NCERT's Class 7 book calls these letters letter-numbers. The Class 9 book gives the more common name, variables. The two words mean the same thing. A number written in front of a variable, like the 12 in 12n, is its coefficient.
A small example
A taxi charges 50 rupees to start and 15 rupees for each kilometre. Let k be the number of kilometres. The fare is 50 + 15k rupees.
- For k = 4, the fare is 50 + 15 × 4 = 110 rupees.
- For k = 10, the fare is 50 + 15 × 10 = 200 rupees.
The rule stays the same. Only the value of the variable changes. Putting a number in place of the letter is called substitution.
Why it matters later
Class 10 Chapter 3 works with a pair of linear equations in two variables, x and y. Every answer there starts with a line such as "Let the cost of one pen be x rupees". Saying clearly what each variable stands for is the first step of the working.
Sources
Facts last checked against these sources on 30 September 2026.
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