Understanding GCF or HCF and LCM Class 4 -Mathematics

GCF or HCF = Greatest Common Factor or Highest Common Factor
LCM= Lowest Common Multiple.
GCF : To understand GCF I illustrate an example. Suppose we need to calculate the GCF of two numbers of 16 and 18 , then first we write the factors of each number as tabulated below.

Numbers	Factors
16	1	2	4	8	16
18	1	2	3	6	9	18

Therefore we can define that the factor which is the greatest one and also common among the numbers are the GCF of those numbers.In the above two rows related to 16 and 18 we notice that 1 and 2 factors are common in the two numbers. But 2 is the greatest common factor. Therefore 2 is the GCF of  16 and 18. 
Let us take another example. This is tabulated below. The common factors of 36 and 48 are 1,2,3,4,and 12. But 12 is the greatest one. Therefore GCF of 36 and 48 is 12. 

Numbers
36	1	2	3	4	6	12	18	36
48	1	2	3	4	6	8	12	16	24	48

LCM: To understand LCM (Lowest Common Multiple) an example is illustrated here. Suppose we need to find out the LCM of two numbers 6 and 9. First of all we multiply these numbers by 1,2,3,4,5 and so on one by one to get the multiples of these numbers. See the table below.

Numbers	multiples
6	6	12	18	24	30	36	42
9	9	18	27	36	45	54	63

Therefore the LCM of 6 and 9 is 18 because it is lowest than next common multiple i.e. 36

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Unitary Method For Class or Grade 4 - Mathematics

Unitary Method is that in which for further calculation value of unit (1) is required for further calculation.

Unit means one,  mathematically '1'. A, An or Per also mean '1'.
If we know the value of one then to find value of many we do MULTIPLICATION. Read this problem and the table.
Problem 1: Cost of one mango is $ 4. Find the cost of 8 mangoes.-

One	Many
1	8
$ 4	?

Solution: 
As the Cost of 1 mango is $ 4. 
Therefor the cost of 8 mangoes is 8x4 = $ 32
Also Watch solution in the video given at the bottom .

If we know the value of many then to find value of one we do DIVISION. Read this problem.
Problem 2: Cost of one mango is $ 4. Find the cost of 8 mangoes.-

Many	One
8	1
$ 40	?

Solution: 
As the Cost of 8 mango is $ 40. 
Therefor the cost of 1 mango is 40/8 = $ 5
Also Watch solution in the video given at the bottom .
If we know the value of many then to find value of many we first need to calculate the value of 1. 
Note:  students of lower classes faces more difficulties in this type of sum of unitary method. But it is very easy. The s only need to know the atone two methods. Because this sum is the combination of the above two methods.
 Read this problem.
Problem 2: Cost of 8 mangos is $ 40. Find the cost of 4 mangoes.-
Watch solution in the video.given at the bottom .

Many	Many
8	4
$ 40	?

Solution: 
As the Cost of 8 mango is $ 40. 
Therefor the cost of 1 mango is 40/8 = $ 5
Therefor the cost of 4 mango is 4x5  = $ 20
Also Watch solution in the video.

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