NCERT Exemplar Solutions
Class 6 - Mathematics - Unit 1: Number System - Problems and Solutions

Question 193

Goal: Use stamps of one value to make Rs 20, Rs 28, and Rs 36 exactly.

This value must divide all three numbers. So find the HCF/ GCD of 20, 28, 36.

Step 1: Prime factorize each amount

\(20 = 2 \times 2 \times 5\)

\(28 = 2 \times 2 \times 7\)

\(36 = 2 \times 2 \times 3 \times 3\)

Step 2: Take only the primes common to all

Common primes: \(2\) and \(2\)

Step 3: Multiply the common primes

\(2 \times 2 = 4\)

Conclusion

The greatest stamp value that fits all is \(\boxed{4}\). So denomination needed = Rs 4.