Choosing digits with the same tens and units difference gives 1-digit difference, like 1 and 2 (21–12 = 9). Class 5 Maths Mela Chapter 1 shows repeated subtraction gives 9 when digits are reversed.
Class 5 Mathematics Maths-Mela Chapter 1 We the Travellers — 1 question answer
Class 5 NCERT Maths-Mela Chapter 1 We the Travellers — I solution
Class 5 Maths Mela Chapter 1: We the Travellers — I explains that using close digits like 1 and 2 or 3 and 4 results in a 1-digit difference (21–12 = 9, 43–34 = 9). This happens because the difference between the two-digit numbers is small. The pattern shows that subtraction of such digit reversals eventually leads to the number 9 quickly.
For more NCERT Solutions for Class 5 Mathematics Maths-Mela Chapter 1: We the Travellers — I Extra Questions & Answer:
https://www.tiwariacademy.com/ncert-solutions/class-5/maths/