Question

Megha wants to mail three parcels to three schools. She finds that the postal charges are ₹20, ₹28, and ₹36, respectively. If she wants to buy stamps of only one denomination, what is the greatest denomination of the stamps that she must buy to mail the three parcels?

• A. ₹4
• B. ₹8
• C. ₹2
• D. ₹1

Answer 1

The correct option is A ₹4

To find the greatest denomination, we should find the HCF (highest common factor) of the given numbers.
HCF of numbers can be found by writing the common prime factors of each number and multiplying them.
Prime factorisation of the numbers:
Prime factorisation of 20 = 2 × 2 × 5
Prime factorisation of 28 = 2 × 2 × 7
Prime factorisation of 36 = 2 × 2 × 3 × 3
Common factors of 20, 28, and 36 = 2 × 2.
HCF of 20, 28, and 36 = 2 × 2 = 4
The greatest denomination of the stamps Megha must buy to mail the three parcels is ₹4.