Expressions Using Letter-Numbers — Class 7 Mathematics

This chapter introduces algebra by using letters to stand for numbers. A letter such as or used to represent a number is called a letter-number (a variable). For example, if Aftab's age is and Shabnam is 3 years older, then Shabnam's age is ; substituting gives . Expressions containing letter-numbers, like or , are called algebraic expressions, and replacing the letter by a number to compute a value is called substitution. You learn to translate word relationships into expressions, to read patterns in sequences (the th multiple of 4 is ; the th even number is ; the th odd number is ), and to use these generalisations to explain why a pattern holds. The power of letter-numbers is that one short expression captures infinitely many cases at once, making it possible both to predict values and to justify mathematical claims — a major step beyond arithmetic.