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Example 2: The LCM of 165 and 275 is 825. Find their HCF.
Solution: Given, two numbers are 165 and 275 and their LCM = 825.

st
nd
We know that, HCF × LCM = 1 number × 2 number
HCF × 825 = 165 × 275
HCF × 825 = 45375

HCF = 45375 = 55
825
Thus, the HCF of 165 and 275 is 55.

Teacher’s Explain to the children that HCF of two co-prime number is 1 and LCM of two co-prime numbers is the product
Tip of that numbers. And if a number is factor of another number, then their HCF is the smaller number and LCM

is the greatest number.
Practice Time 3G

1. Complete the table:

HCF LCM Product of two numbers
(a) 12 324
(b) 4 252

(c) 72 864
(d) 50 300
2. Find the LCM of two numbers, if their product is 225 and the HCF is 9.

3. The HCF of two numbers is 15 and LCM is 45. If one of the numbers is 27, find the
other.
4. The product of two numbers is 450. Find their LCM if their HCF is 15.
5. If the LCM of two numbers is 120 and their product is 1800, what will be the HCF?

Brain Sizzlers

1. I am a 3-digit number. The sum of my digits is 5 and I am prime too. If my ones
and hundreds digits are interchanged, I still remain prime. Who am I?

2. There are 360 erasers and 456 sharpeners. These articles are to be arranged in
piles containing the same number of articles. Find the greatest number of articles
possible in each pile. Also, find the number of piles formed.

76 Mathematics-5