NCERT Book Class 7 Mathematics (Part I) Chapter 4 Expressions using Letter-Numbers

EXPRESSIONS
4 USING LETTER-
NUMBERS

4.1 The Notion of Letter-Numbers
In this chapter we shall look at a concise way of expressing mathematical
relations and patterns. We shall see how this helps us in thinking about
these relationships and patterns, and in explaining why they may hold
true.
Example 1: Shabnam is 3 years older than Aftab. When Aftab’s age
10 years, Shabnam’s age will be 13 years. Now Aftab’s age is 18 years,
what will Shabnam’s age be? _______

Given Aftab’s age, how will you find out Shabnam’s age?
Easy: We add 3 to Aftab’s age to get Shabnam’s age.
Can we write this as an expression?
Shabnam’s age is 3 years more than Aftab’s. In short, this can be
written as:
Shabnam’s age = Aftab’s age + 3.
Such mathematical relations are Aftab’s Expression for
generally represented in a shorthand age Shabnam’s age
form. In the relation above, instead 4 4 + 3
of writing the phrase ‘Aftab’s Age’,
the convention is to use a convenient 10 10 + 3
symbol. Usually, letters or short phrases 23 23 + 3
are used for this purpose. ? ? + 3
Let us say we use the letter a to
denote Aftab’s age (we could have a a + 3
used any other letter), and s to denote
Fig. 4.1
Shabnam’s age. Then the expression to
find Shabnam’s age will be a + 3, which can be written as
s = a + 3.
If a is 23 (Aftab’s age in years), then what is Shabnam’s age?