LCM and HCF


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H.C.F and L.C.M


Highest Common Factor (H.C.F)

H.C.F is the highest common factor or also known as greatest common divisor, the greatest number which exactly divides all the given numbers.
There are two methods to find H.C.F of given numbers, they are:
i. Prime factorization method.
ii. Division Method.

HCF of given fractions
H.C.F of given fractions =
L.C.M of denominator
H.C.F of numerator


Least Common Multiple (L.C.M)

L.C.M is least common multiple, the smallest number which is exactly divisible by all the given numbers.
There are two methods to find L.C.M of given numbers, they are:
i. Prime factorization method.
ii. Division Method.

LCM of given fractions
L.C.M of given fractions =
H.C.F of denominator
L.C.M of numerator


Important Points

1. Product of two numbers = H.C.F *L.C.M of the two numbers

2. The smallest number which when divided by x, y and z leaves a remainder R in each case.
Required number = (L.C.M of x, y, z) + R

3. The greatest number which divides x, y and z to leave the remainder R is H.C.F of (x - R), (y - R) and (z - R)

4. The greatest number which divide x, y, z to leave remainders a, b, c is H.C.F of (x - a), (y - b) and (z - c)

5. The smallest number which when divided by x, y and z leaves remainder of a, b, c (x - a), (y - b), (z - c) are multiples of K
Required number = (L.C.M of x, y and z) - K


6. The LCM will be the product of multiplying the highest power of each prime number together.example: lcm(8,9,21) ,The highest power of the three prime numbers 2, 3, and 7 is 23, 32, and 71, respectively. Thus,lcm = 8*9*7 =504

7. The HCF can be computed by determining the prime factorizations of the two numbers and comparing factors, example:hcf(18, 84), prime factors 18 = 2 * 32 and 84 = 22 * 3 * 7 and notice that the "overlap" of the two expressions is 2 * 3; so hcf = 6.