what is the difference between H.C.F and L.C.M
Answers
Answer:
HCF= highest common factor. It is the greatest number which divides the two or more given numbers. The LCM of two or more numbers is the smallest number that is a common multiple of two or more numbers.
Step-by-step explanation:
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Answer:
HCF And LCM
These are very simple and important topics. The trend has been to ask questions from this section quite frequently nowadays. Although the questions asked will not be direct, it will be a indirect question and thus the biggest challenge in an exam for this topic lies in identification of the question and that it is asked from this topic. Solving a problem after identification is easy.
Note: Calculation speed is very important for this topic esp. division with prime nos. like 2,3 ,7 etc for factorization.
Let’s start with very basic concepts and then go to HCF and LCM.
FACTOR
A factor of a given number is every number that divides exactly into that number.
Example
Write down all factors of 10.
10 = 2 x 5, so numbers 2 and 5 are factors of 10.
Also 10 = 10 x 1, so 10 and 1 are factors of 10.
The factors of 10 are 1, 2, 5, and 10.
NOTE: Number 1 and the number itself are always factors of any number.
PRIME AND COMPOSITE NUMBERS
A prime number has exactly 2 factors, the number itself and 1.
In other words, the prime number can be divided only by 1 and by itself.
NOTE: 0 and 1 are not prime numbers.
Example: 5 is a prime number, because the only factors it has are 1 and 5.
The prime numbers less than 20 are 2,3,5,7,11,13,17,19
Example:
Find all prime factors of 30.
Solution:
All the factors of 30 are 30, 15, 10, 6, 5, 3, 2, 1
But only 5, 3 and 2 are prime numbers.
Thefore all prime factors of 30 are 2, 3 and 5.
A composite number has at least one more factor that the number itself or 1.
In fact, all whole numbers that are not prime are composite except for 1 and 0, which are not prime and not composite.
The composite numbers less than 20 are 4, 6, 8, 9, 10, 12, 14, 15, 16, and 18.
DIVISIBILITY RULES
The simple divisibility rules will help you to find factors of a number.
The number is divisible by:
• 2 if the last digit is 0, 2, 4, 6, or 8 (example: 12346);
• 3 if the sum of digits in the number are divisible by 3
(example: 1236, because 1+2+3+6 = 12 = 3 x 4);
• 4 if the last 2 digits are divisible by 4
(example: 897544, because 44 = 4 x 11);
• 5 if the last digit is 0 or 5
(example: 178965 or 40980);
• 6 if it is divisible by 2 and 3;
• 8 if the last 3 digits are divisible by 8
(example: 124987080, because 080 = 8 x 10;
• 9 if the sum of digits is divisible by 9
(example: 234612, because 2+3+4+6+1+2 = 18 = 9 x 2);
• 10 if the last digit is 0
(example: 99990 );
• 11 if the difference between sum of digits in odd and sum of digits in even places is 0 or a multiple of 11.
• 12 if the no is divisible by both 3 and 4.
• 19 if the no of tens added to twice the no of ones is divisible by 19.
(Example: 228; no of tens =22; no of ones = 8; the required sum = 22+ 2×8 =38; hence, 228 is divisible by 19)
• 25 if the no formed by the last two digits (ie digits at tens and ones place) is divisible by 25.
(Example: 31243482325; no formed by last two digits =25;
hence 31243482325 is divisible by 25)
• 100 if the last 2 digits are 0
(example 987600);
• 125 if the no formed by last 3 digits is divisible by 125.
(Note: there are some complex divisibility tests for 7, 13 and 17 too but I recommend not to follow them as dividing the no given would be easier and faster than applying those divisibility tests.)
NOTE: If a number is divisible by 2 factors, it is also divisible by the product of these factors.
Example 1: Number 18 is divisible by 2 and 3, so it must be divisible by 2 x 3 = 6.
Example 2: Number 945 is divisible by 9 (why?) and by 5 (why?), so it must be divisible by 9 x 5 = 45. (Can you check it?)
COMMON FACTORS
When two (or more) numbers have the same factor, that factor is called a common factor.
Example
Find all the common factors of 12 and 18.
Factors of 12 are 1, 2, 3, 4, 6, 12.
Factors of 18 are 1, 2, 3, 6, 18.
The common factors of 12 and 18 are 1, 2, 3 and 6.
HIGHEST COMMON FACTOR (H.C.F)
The Highest Common Factor (H.C.F) of two (or more) numbers is the largest number that divides evenly into both numbers. It is also known as G.C.D. (Greatest common divisor)
In other words the H.C.F is the largest of all the common factors.
The common factors or of 12 and 18 are 1, 2, 3 and 6.
The largest common factor is 6, so this is the H.C.F. of 12 and 18.
It is very easy to find a H.C.F. of small numbers, like 6 and 9 (it is 3) or 8 and 4 (it is 4).
The best way is to keep finding the factors of the smaller number, starting from the largest factor. The first factor of the smaller number that is also a factor of the larger number is a H.C.F.
LEAST COMMON MULTIPLE (L.C.M.)
A common multiple is a number that is a multiple of two or more numbers. The common multiples of 3 and 4 are 0, 12, 24…
The least common multiple (LCM) of two numbers is the smallest number (not zero) that is a multiple of both.
Concept – Prime Factorisation