Three pieces of 1/12 make 1/4. Dividing a whole into 12 equal parts, three of them together equal one-fourth of the whole. So, 1/4 = 3/12.
Class 5 NCERT Maths-Mela Chapter 2 Fractions solution
class 5 Maths-Mela Mathematics Textbook Chapter 2 Fractions question answer
When a whole is divided into 12 equal parts, each piece is 1/12. If I collect 3 of them, I cover exactly one-fourth of the whole. So, 1/4 = 3/12. The same can be seen using diagrams or the fraction kit. One-fourth and three twelfths are just different names for the same part of the whole.
For more NCERT Solutions for Class 5 Mathematics Maths-mela Chapter 2: Fractions Extra Questions & Answer:
https://www.tiwariacademy.com/ncert-solutions/class-5/maths/maths-mela-chapter-2/