NCERT Solutions Ganita Prakash (Part 1) Chapter 4 In-text Questions — The Notion of Letter-Numbers
Book page 82 Updated on2026-09-05
Q1.
Given the age of Shabnam, write an expression to find Aftab’s age.
Answer
Aftab is 3 years younger, so subtract 3.
Aftab's age = Shabnam's age – 3 a = s – 3
Why it happens:s = a + 3 and a = s – 3 say the same thing from the two ends. Adding 3 and subtracting 3 undo each other.
Q2.
Use this expression to find Aftab’s age if Shabnam’s age is 20.
Answer
Replace s by 20.
a = s – 3 = 20 – 3 = 17 years
Check it yourself: Now go back — s = a + 3 = 17 + 3 = 20. It matches.
Q3.
Example 2: Parthiv is making matchstick patterns. He repeatedly places Ls next to each other. Each L has two matchsticks as shown in Figure 4.2. How many matchsticks are needed to make 5 Ls? 7 Ls? 45 Ls? Now, what is the relation between the number of Ls and the number of sticks?
Answer
Every L uses exactly 2 matchsticks, so the count is always double the number of Ls.
5 Ls → 5 × 2 = 10 matchsticks 7 Ls → 7 × 2 = 14 matchsticks 45 Ls → 45 × 2 = 90 matchsticks
In words: Number of matchsticks = 2 × Number of L’s. Taking n for the number of Ls, the expression is
2 × n
Why it happens: The Ls do not share any matchstick — each one is separate. So the total is simply 2 counted n times, which is 2 × n.